int Merage = 2;
for (int j = 2; j <= sheet.LastRowNum; j++)
{
if (j > 2 && sheet.GetRow(j).GetCell(0).StringCellValue != sheet.GetRow(j - 1).GetCell(0).StringCellValue)
{
sheet.AddMergedRegion(new CellRangeAddress(Merage, j - 1, 0, 0));
//sheet.GetRow(j).GetCell(1).SetCellValue(j);
Merage = j;
}
}
sheet.AddMergedRegion(new CellRangeAddress(Merage, sheet.LastRowNum, 0, 0));