string sFileName = sFilePath;
            FileStream myFile = new FileStream(sFileName, FileMode.Open, FileAccess.Read);
            HSSFWorkbook workbook = new HSSFWorkbook(myFile);
            ISheet sheet = workbook.GetSheetAt(0);
            if (sheet != null)
            {
                ClearCellsValusBeforeMerge(sheet, 1, 2, 1, 2);
                sheet.AddMergedRegion(new CellRangeAddress(1, 2, 1, 2));
            }
            FileStream savefile = new FileStream(sFileName, FileMode.Create);
            workbook.Write(savefile);
            savefile.Close();

/// <summary>
        /// 合并前先清空该合并区域的数据
        /// 跳过左上角的数据，清空区域其他数据
        /// </summary>
        /// <param name="sheet">sheet</param>
        /// <param name="iRowFrom">行头</param>
        /// <param name="iRowTo">行尾</param>
        /// <param name="iColFrom">列头</param>
        /// <param name="iColTo">列尾</param>
        private static void ClearCellsValusBeforeMerge(ISheet sheet, int iRowFrom, int iRowTo, int iColFrom, int iColTo)
        {
            if (sheet != null)
            {
                for (int i = iRowFrom; i <= iRowTo; i++)
                {
                    for (int j = iColFrom; j <= iColTo; j++)
                    {
                        if (i == iRowFrom && j == iColFrom) continue;
                        sheet.GetRow(i).Cells[j].SetCellValue("");
                    }
                }
            }
        }