app.Quit();
            app = null;           
        }
    }
} 

二、读取到dataset中/从dataset中写入sql server：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using Microsoft.Office.Interop.Excel;
using System.Data.OleDb;

namespace ExcelDemo
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 读取Excel文档
        /// </summary>
        /// <param name="Path">文件名称</param>
        /// <returns>返回一个数据集</returns>
        public DataSet ExcelToDS(string Path)
        {
            string strConn = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + Path + ";" + "Extended Properties=Excel 8.0;";
            OleDbConnection conn = new OleDbConnection(strConn);
            conn.Open();
            string strExcel = "";
            OleDbDataAdapter myCommand = null;
            DataSet ds = null;
            strExcel = "select * from [Recovered_Sheet1$]";
            myCommand = new OleDbDataAdapter(strExcel, strConn);
            ds = new DataSet();
            myCommand.Fill(ds);
            return ds;
        }