根据简短的网页搜索，word和excel的正确MIME类型是：

According to a brief web search, the correct mime types for word and excel are:

application/vnd.openxmlformats-officedocument.wordprocessingml.document
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet

http://www.bram.us/2007/05/25/office-2007-mime-types-for-iis/

编辑：

以下简化示例适用于我。它与你的不同之处在于它使用通用处理程序而不是Web表单（这更适合这样的东西）。

The following simplified sample works for me. It is different from yours in that it uses a generic handler instead of a web form (which is more appropriate for something like this anyway).

要测试它，请确保在应用程序的***文件夹中有一个名为Book1.xlsx的excel 2007文件。

To test it, make sure there is an excel 2007 file named Book1.xlsx in the top level folder of the application.

DownloadSpreadsheet.ashx:

<%@ WebHandler Language="C#" Class="DownloadSpreadsheetHandler" %>

using System;
using System.Web;
using System.IO;

public class DownloadSpreadsheetHandler: IHttpHandler {

    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
        string path = context.Server.MapPath("~/Book1.xlsx");
        using (FileStream spreadsheet = File.OpenRead(path))
        {
            CopyStream(spreadsheet, context.Response.OutputStream);
        }
    }

    public bool IsReusable {
        get {
            return false;
        }
    }

    private static void CopyStream(Stream input, Stream output)
    {
        byte[] buffer = new byte[32768];
        while (true)
        {
            int read = input.Read(buffer, 0, buffer.Length);
            if (read <= 0)
                return;
            output.Write(buffer, 0, read);
        }
    }

}