fs = new FileStream(fileName, FileMode.OpenOrCreate, FileAccess.ReadWrite);

if (fileName.IndexOf(".xlsx") > 0) // 2007版本
                workbook = new XSSFWorkbook();
            else if (fileName.IndexOf(".xls") > 0) // 2003版本
                workbook = new HSSFWorkbook();

                //头部样式
                ICellStyle headcellStyle = workbook.CreateCellStyle();
                headcellStyle.BorderBottom = NPOI.SS.UserModel.BorderStyle.Thin;
                headcellStyle.BorderLeft = NPOI.SS.UserModel.BorderStyle.Thin;
                headcellStyle.BorderRight = NPOI.SS.UserModel.BorderStyle.Thin;
                headcellStyle.BorderTop = NPOI.SS.UserModel.BorderStyle.Thin;
                headcellStyle.FillBackgroundColor = HSSFColor.Black.Index;
                headcellStyle.FillPattern = FillPattern.SolidForeground;
                headcellStyle.FillForegroundColor = HSSFColor.Orange.Index;

sheet = workbook.CreateSheet(sheetName);

IRow row = sheet.CreateRow();

ICell icell1top = row.CreateCell(j);

icell1top.CellStyle = headcellStyle;
icell1top.SetCellValue(data.Columns[j].ColumnName);