NPOI创建的单元格被空白的覆盖

#region///写入数据
                int RowCount2 = ds.Tables["t10"].Rows.Count;
                for (i = 0; i < RowCount2; i++)
                {
                    sheet.CreateRow(i + 2).CreateCell(0).SetCellValue(i + 1);
                    int t = 0;
                    for (int j = 0; j < rowCount; j++)
                    {
                        if (SelectItem.Items[j].Selected)
                        {
                            string sel = SelectItem.Items[j].Value.TrimEnd();
                            IRow rowMin1 = sheet.CreateRow(rowMin + 1 + i);
                            if(sel=="Sex")
                            {
                                if (ds.Tables["t10"].Rows[i][sel].ToString() == "1")
                                    rowMin1.CreateCell(colMin + t).SetCellValue("男");
                                else
                                    rowMin1.CreateCell(colMin + t).SetCellValue("女");
                            }
                            else if (sel == "GradeName" && ds.Tables["t11"].Rows[j]["ItemName"].ToString().TrimEnd() != "年级")
                            {
                                rowMin1.CreateCell(colMin + t).SetCellValue("'" + ds.Tables["t10"].Rows[i][sel].ToString() + ".9");
                            }
                            else
                            {
                                rowMin1.CreateCell(colMin + t).SetCellValue("'" + ds.Tables["t10"].Rows[i][sel]);
                            }
                            if (Price(S_ID)>0)
                            {
                                rowMin1.CreateCell(colMin + 1 + t).SetCellValue(Price(S_ID));
                            }
                            sheet.AutoSizeColumn(colMin + t);     //自动适应宽度
                            sheet.AutoSizeColumn(colMin + 1 + t); //自动适应宽度
                            t++;
                        }
                    }
                }
                #endregion
人家告诉我是因为重新创建了行才被覆盖了，不过我不懂是怎样覆盖的

补充：.NET技术 ,  ASP.NET