注意，Excel读入DataTable需要使用NPOI包

/// <summary>
  /// Excel导入成Datable
  /// </summary>
  /// <param name="file">导入路径(包含文件名与扩展名)</param>
  /// <returns></returns>
  public static DataTable ExcelToTable(string file, string sheetName = "")
  {
    DataTable dt = new DataTable();
    IWorkbook workbook = null;
    try
    {

      string fileExt = Path.GetExtension(file).ToLower();
      using (FileStream fs = new FileStream(file, FileMode.Open, FileAccess.Read))
      {
        //XSSFWorkbook 适用XLSX格式，HSSFWorkbook 适用XLS格式
        if (fileExt == ".xlsx") { workbook = new XSSFWorkbook(fs); } else if (fileExt == ".xls") { workbook = new HSSFWorkbook(fs); } else { workbook = null; }
        if (workbook == null) { return null; }

        ISheet sheet = string.IsNullOrWhiteSpace(sheetName) ? workbook.GetSheetAt(0) : workbook.GetSheet(sheetName);

        //表头  
        IRow header = sheet.GetRow(sheet.FirstRowNum);
        if (header == null)
        {
          throw new Exception("Excel表没有数据，请添加数据");
        }
        List<int> columns = new List<int>();
        for (int i = 0; i < header.LastCellNum; i++)
        {
          object obj = GetValueType(header.GetCell(i));
          if (obj == null || obj.ToString().Trim() == string.Empty)
          {
            continue;
          }
          else
          {
            dt.Columns.Add(new DataColumn(obj.ToString()));
          }
          columns.Add(i);
        }
        //数据  
        for (int i = sheet.FirstRowNum + 1; i <= sheet.LastRowNum; i++)
        {
          DataRow dr = dt.NewRow();
          bool hasValue = false;
          foreach (int j in columns)
          {
            if (sheet.GetRow(i) != null) {
              dr[j] = GetValueType(sheet.GetRow(i).GetCell(j));
            }
            
            //if (dr[j] != null && dr[j].ToString() != string.Empty)
            //{
            //  hasValue = true;
            //}
          }
          //if (hasValue)
          //{
          //  dt.Rows.Add(dr);
          //}
          dt.Rows.Add(dr);

        }
        dt.AcceptChanges();

      }
      return dt;
    }
    catch (Exception e)
    {
      return null;
    }
    finally
    {
      if (dt != null) { dt.Dispose(); }
      if (workbook != null) { workbook = null; }
    }
  }
  /// <summary>
  /// 获取单元格类型
  /// </summary>
  /// <param name="cell"></param>
  /// <returns></returns>
  private static object GetValueType(ICell cell)
  {
    if (cell == null)
      return null;
    switch (cell.CellType)
    {
      case CellType.Blank: //BLANK:  
        return "";
      case CellType.Boolean: //BOOLEAN:  
        return cell.BooleanCellValue;
      case CellType.Numeric: //NUMERIC:  
        return cell.NumericCellValue;
      case CellType.String: //STRING:  
        return cell.StringCellValue;
      case CellType.Error: //ERROR:  
        return cell.ErrorCellValue;
      case CellType.Formula: //FORMULA:  
      default:
        return "=" + cell.CellFormula;
    }
  }

DataTable读入Excel

/// <summary>
		/// Datatable生成Excel表格并返回路径
		/// </summary>
		/// <param name="m_DataTable">Datatable</param>
		/// <param name="s_FileName">文件名</param>
		/// <returns></returns>
		public static string DataToExcel(System.Data.DataTable m_DataTable, string s_FileName)
		{
			//string FileName = @"C:\Users\JK\Desktop\DataTableToExcel\" + s_FileName + ".xlsx";  //文件存放路径
			string FileName = s_FileName;
			if (System.IO.File.Exists(FileName))                                //存在则删除
			{
				System.IO.File.Delete(FileName);
			}
			System.IO.FileStream objFileStream;
			System.IO.StreamWriter objStreamWriter;
			string strLine = "";
			objFileStream = new System.IO.FileStream(FileName, System.IO.FileMode.OpenOrCreate, System.IO.FileAccess.Write);
			objStreamWriter = new System.IO.StreamWriter(objFileStream, Encoding.Unicode);
			for (int i = 0; i < m_DataTable.Columns.Count; i++)
			{
				strLine = strLine + m_DataTable.Columns[i].Caption.ToString() + Convert.ToChar(9);      //写列标题
			}
			objStreamWriter.WriteLine(strLine);
			strLine = "";
			for (int i = 0; i < m_DataTable.Rows.Count; i++)
			{
				for (int j = 0; j < m_DataTable.Columns.Count; j++)
				{
					if (m_DataTable.Rows[i].ItemArray[j] == null)
						strLine = strLine + " " + Convert.ToChar(9);                                    //写内容
					else
					{
						string rowstr = "";
						rowstr = m_DataTable.Rows[i].ItemArray[j].ToString();
						if (rowstr.IndexOf("\r\n") > 0)
							rowstr = rowstr.Replace("\r\n", " ");
						if (rowstr.IndexOf("\t") > 0)
							rowstr = rowstr.Replace("\t", " ");
						strLine = strLine + rowstr + Convert.ToChar(9);
					}
				}
				objStreamWriter.WriteLine(strLine);
				strLine = "";
			}
			objStreamWriter.Close();
			objFileStream.Close();
			return FileName;        //返回生成文件的绝对路径
		}