public partial class mergeExcel_WebForm4 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            Excel.Application app = new Excel.Application();            Excel._Workbook result = app.Workbooks.Add();
            Excel._Workbook wb1 = app.Workbooks.Open(Path.GetFullPath(@"D:/zjj/a.xlsx"));
            Excel._Workbook wb2 = app.Workbooks.Open(Path.GetFullPath(@"D:/zjj/b.xlsx"));            foreach (Excel._Worksheet each in wb1.Sheets)
            {
            
                   each.Copy(result.Worksheets[1]);
            }            foreach (Excel._Worksheet each in wb2.Sheets)
            {
                    each.Copy(result.Worksheets[1]);
            }             result.SaveAs(@"D:\zjj\result.xlsx");            Response.Write("<script>alert('merge successfully');</script>");
            wb1.Close();
            wb2.Close();
            app.Quit();