在这里找到答案，

if (xlWorkbook != null && xlWorkbook.Sheets.Count > 0)
{
         Excel._Worksheet xlWorksheet = (Excel._Worksheet)xlWorkbook.Sheets[1];

         //B8 position an column "IndentValue" in inserted 
         Excel.Range oRng = xlWorksheet.Range["B8"];
         oRng.EntireColumn.Insert(Excel.XlInsertShiftDirection.xlShiftToRight,
         Excel.XlInsertFormatOrigin.xlFormatFromRightOrBelow);
         oRng = xlWorksheet.Range["B8"];
         oRng.Value2 = "IndentValue";

         //collect indent value of Col A in Col B
         for (i = 9; i <= xlWorksheet.UsedRange.Rows.Count; i++)
         {
             Excel.Range aRng = xlWorksheet.Range["A" + i];
             var Indentvalue = aRng.IndentLevel;
             xlWorksheet.Cells[i, 2].value = Indentvalue;
          }

         Excel.Range xlHeaderRange = xlWorksheet.UsedRange;

         object[,] excelObj = (object[,])xlHeaderRange.Value2;

         string filename = Path.GetFileNameWithoutExtension(sFile);

         if (staticconstList.Contains(filename))
           {
               if (effectiveDate == DateTime.MinValue)
                {
                    DateTime.TryParse(Convert.ToString((xlWorksheet.Cells[Definition.DATE_ROW_ID, Definition.DATE_COLUMN_ID] as Excel.Range).Value), out effectiveDate);
                }

                 xlWorkbook.Saved = true;
                 xlWorkbook.Close();
            }
}