New Post: How to append datatable to an exist excel file?

I have to write a datatable into an exist excel file which is not empty, the columns of the datatable and the sheet of the file are the same, how can I do this? I tried the append mode, like this:

            FileStream file = new FileStream(FileName, FileMode.Append);
            hssfworkbook.Write(file);

but nothing happens, Is there anything wrong? Thank you.