Code
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.OleDb;

namespace yournamespace
{
    class excel
    {
        //从Excel文件导入到DataSet
        #region 从Excel文件导入到DataSet
        /// 从指定的Excel文件导入
        public static DataSet ImportFromExcel(string strFileName)
        {
            DataSet ds = new DataSet();
            ds = doImport(strFileName, "[Sheet1$]");
            return ds;
        }
        public static DataSet ImportFromExcel(string strFileName, string strSheetName)
        {
            DataSet ds = new DataSet();
            ds = doImport(strFileName, strSheetName);
            return ds;
        }

        /// 执行导入
        private static DataSet doImport(string strFileName, string strSheetName)
        {
            if (strFileName == "") return null;
            string strConn = "Provider=Microsoft.Jet.OLEDB.4.0;" +
             "Data Source=" + strFileName + ";" +
             "Extended Properties=Excel 8.0;";
            OleDbDataAdapter ExcelDA = new OleDbDataAdapter("SELECT * FROM " + strSheetName.Trim(), strConn);
            DataSet ExcelDs = new DataSet();
            try
            {
                ExcelDA.Fill(ExcelDs, "ExcelInfo");

            }
            catch (Exception err)
            {
                System.Console.WriteLine(err.ToString());
            }
            return ExcelDs;
        }
        #endregion

        internal static DataSet ImportFromExcel(string strFileName, string strSheetName, string pass)
        {
            if (strFileName == "") return null;
            string strConn = "Provider=Microsoft.Jet.OLEDB.4.0;" +
             "Data Source=" + strFileName + ";" +
             "Extended Properties=Excel 8.0;P="+pass+";";
            DataSet ExcelDs = new DataSet();
            try
            {
                OleDbDataAdapter ExcelDA = new OleDbDataAdapter("SELECT * FROM " + strSheetName.Trim(), strConn);


                ExcelDA.Fill(ExcelDs, "ExcelInfo");

            }
            catch (Exception err)
            {
                System.Console.WriteLine(err.ToString());
            }
            return ExcelDs;
        }
    }
}

using mExcel = Microsoft.Office.Interop.Excel;

string fileName = Server.MapPath("sample.xls");
            if (!File.Exists(fileName))
                return;

            mExcel.Application mApp = new mExcel.Application();
            mExcel.Workbook mBook = mApp.Workbooks.Open(fileName, Missing.Value, Missing.Value, Missing.Value,
                Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);
            mExcel.Worksheet mSheet = mBook.Worksheets[1] as mExcel.Worksheet;

            mExcel.Range mRange = mSheet.get_Range("A1", "E12");

            Array mArray = mRange.Formula as Array;

            mBook.Close(false, null, null);
            mApp.Quit();

            mRange = null;
            mSheet = null;
            mBook = null;
            mApp = null;


            if (mArray != null)
            {
                StringBuilder sBuilder = new StringBuilder();
                int cells = mArray.GetLength(0);
                int rows = mArray.GetLength(1);

                for (int i = 1; i <= cells; i++)
                {
                    for (int j = 1; j <= rows; j++)
                    {
                        sBuilder.Append(mArray.GetValue(i, j) + "    ");
                    }
                    sBuilder.Append("<br/>");
                }

                Response.Write(sBuilder.ToString());
            }