using NPOI.SS.UserModel;

                    IWorkbook workbook = WorkbookFactory.Create(importExcelPath);
                    ISheet ISheetsheet = workbook.GetSheetAt(0);//获取第一个工作薄
                    IRow row = (IRow)sheet.GetRow(0);//获取第一行
                    sheet.GetRow(1).GetCell(0).SetCellValue(userName);
                    sheet.GetRow(1).GetCell(1).SetCellValue(passWord);
                    using (var fs = File.OpenWrite(importExcelPath))
                    {
                        workbook.Write(fs);//向打开的这个xls文件中写入数据  
                    }