先设置日期格式，再加载数据。

//Create the worksheet
string sheetName = string.IsNullOrEmpty(sourceTable.TableName) ? "Sheet1" : sourceTable.TableName;
ExcelWorksheet ws = pck.Workbook.Worksheets.Add(sheetName);
ws.Column(16).Style.Numberformat.Format = "yyyy-MM-dd HH:mm:ss"; //第16列
ws.Column(23).Style.Numberformat.Format = "yyyy-MM-dd HH:mm:ss"; //第23列
ws.Column(30).Style.Numberformat.Format = "yyyy-MM-dd HH:mm:ss"; //第30列
//Load the datatable into the sheet, starting from cell A1. Print the column names on row 1
ws.Cells["A1"].LoadFromDataTable(sourceTable, true);