public partial class FileDownLoad : System.Web.UI.Page        
        {        
                //提供下载的文件，不编码的话文件名会乱码        
string fileName = HttpContext.Current.Server.UrlEncode() string fileName = HttpContext.Current.Server.UrlEncode( "规范.rar");        
string filePath = HttpContext.Current.Server.MapPath() string filePath = HttpContext.Current.Server.MapPath( "规范.rar");        
                //使用TransmifFile下载文件        
void btnDL1_Click() void btnDL1_Click(object sender, EventArgs e)        
                {        
                        FileInfo info = new FileInfo(filePath);        
                        long fileSize = info.Length;        
                        Response.Clear();        
                        Response.ContentType = "application/x-zip-compressed";        
                        Response.AddHeader( "Content-Disposition", "p_w_upload;filename="+ fileName);        
                        //不指明Content-Length用Flush的话不会显示下载进度        
                        Response.AddHeader( "Content-Length", fileSize.ToString());        
                        Response.TransmitFile(filePath, 0, fileSize);        
                        Response.Flush();        
                        Response.Close();        
                }        
    
                //使用WriteFile下载文件        
void btnDL2_Click() void btnDL2_Click(object sender, EventArgs e)        
                {        
                        FileInfo info = new FileInfo(filePath);        
                        long fileSize = info.Length;        
                        Response.Clear();        
                        Response.ContentType = "application/octet-stream";        
                        Response.AddHeader( "Content-Disposition", "attachement;filename=" + fileName);        
                        //指定文件大小        
                        Response.AddHeader( "Content-Length", fileSize.ToString());        
                        Response.WriteFile(filePath, 0, fileSize);        
                        Response.Flush();        
                        Response.Close();        
                }        
    
                //使用OutputStream.Write分块下载文件        
void btnDL3_Click() void btnDL3_Click(object sender, EventArgs e)        
                {        
                        //指定块大小        
                        long chunkSize = 102400;        
                        //建立一个100K的缓冲区        
                        byte[] buffer = new byte[chunkSize];        
                        //已读的字节数        
                        long dataToRead = 0;        
                        FileStream stream = null;        
                        try        
                        {        
                                //打开文件        
                                stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);        
                                dataToRead = stream.Length;        
    
                                //添加Http头        
                                Response.ContentType = "application/octet-stream";        
                                Response.AddHeader( "Content-Disposition", "attachement;filename=" + fileName);        
                                Response.AddHeader( "Content-Length", dataToRead.ToString());        
    
                                 while (dataToRead > 0)        
                                {        
                                         if (Response.IsClientConnected)        
                                        {        
                                                int length = stream.Read(buffer, 0, Convert.ToInt32(chunkSize));        
                                                Response.OutputStream.Write(buffer, 0, length);        
                                                Response.Flush();        
                                                Response.Clear();        
                                                dataToRead -= length;        
                                        }        
                                         else        
                                        {        
                                                //防止client失去连接        
                                                dataToRead = -1;        
                                        }        
                                }        
                        }        
                        catch (Exception ex)        
                        {        
                                Response.Write( "Error:" + ex.Message);        
                        }        
                        finally        
                        {        
                                 if (stream != null)        
                                {        
                                        stream.Close();        
                                }        
                                Response.Close();        
                        }        
                }        
    
                //使用BinaryWrite下载文件，大文件效率不行        
void btnDL4_Click() void btnDL4_Click(object sender, EventArgs e)        
                {        
                        FileStream stream = null;        
                        try        
                        {        
                                //读文件,大文件一次读入会占用大量内存        
                                stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);        
                                byte[] bytes = new byte[stream.Length];        
                                stream.Read(bytes, 0, bytes.Length);        
                                stream.Close();        
    
                                //添加Http头        
                                Response.ContentType = "application/octet-stream";        
                                Response.AddHeader( "Content-Disposition", "attachement;filename=" + fileName);        
                                Response.AddHeader( "Content-Length", bytes.Length.ToString());        
                                Response.BinaryWrite(bytes);        
                                Response.Flush();        
                        }        
                        catch (Exception ex)        
                        {        
                                Response.Write( "Error:" + ex.Message);        
                        }        
                        finally        
                        {        
                                 if (stream != null)        
                                {        
                                        stream.Close();        
                                }        
                                Response.Close();        
                        }        
                }        
                //使用BinaryWrite分块下载文件        
void btnDL5_Click() void btnDL5_Click(object sender, EventArgs e)        
                {        
                        //指定区块和缓冲区        
                        long chunkSize = 102400;        
                        byte[] buffer = new byte[chunkSize];        
                        FileStream stream = null;        
                        long dataToRead = 0;        
                        try        
                        {        
                                stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);        
                                dataToRead = stream.Length;        
                                //添加Http头        
                                Response.ContentType = "application/octet-stream";        
                                Response.AddHeader( "Content-Disposition", "attachement;filename=" + fileName);        
                                Response.AddHeader( "Content-Length", dataToRead.ToString());        
    
                                 while (dataToRead > 0)        
                                {        
                                         if (Response.IsClientConnected)        
                                        {        
                                                int length = stream.Read(buffer, 0, Convert.ToInt32(chunkSize));        
                                                Response.BinaryWrite(buffer);        
                                                Response.Flush();        
                                                Response.Clear();        
    
                                                dataToRead -= length;        
                                        }        
                                         else        
                                        {        
                                                dataToRead = -1;        
                                        }        
                                }        
    
                        }        
                        catch(Exception ex)        
                        {        
                                Response.Write( "Error:" + ex.Message);        
                        }        
                        finally    
                        {        
                                 if (stream != null)        
                                {        
                                        stream.Close();        
                                }        
                                Response.Close();        
                        }        
                }        
        }    
以上除了第四种不推荐以外，其他的都可以，但是个人感觉分块下载的要好一点。没有仔细测试，所以可能有问题。
注意：对于中文文件名要编码才能正确显示。对于 长中文文件名(UTF8编码后大于153字节的中文)即使编码了，还是有问题的，大家可以参考这个链接。 http://hi.baidu.com/river_5566/blog/item/d66804cef8afb031b700c863.html