Sno Sname Class
101 John  1std
102 Mike  1std
103 Sekar 2nd
104 Mathew 3rd

Select Class<asp:DropDownList ID="DropDownList1" runat="server">
    <asp:ListItem>1std</asp:ListItem>
    <asp:ListItem>2nd</asp:ListItem>
    <asp:ListItem>3rd</asp:ListItem>
</asp:DropDownList>
<br />
Select Srudent Name<asp:DropDownList ID="DropDownList2" runat="server">
</asp:DropDownList>
<br />
<asp:Button runat="server" Text="Search" OnClick="Unnamed1_Click" /><br />
<asp:GridView runat="server" ID="gridview">
</asp:GridView>

using System.Data.OleDb;
using System.Data;
using System.Data.SqlClient;
public partial class ExcelSearch : System.Web.UI.Page
{
    DataTable dt = new DataTable();
    DataSet ds = new DataSet();
    string path = @"D:\student.xlsx";
    protected void Page_Load(object sender, EventArgs e)
    {
        //Initially load student name in the second dropdown list from excel sheet
        if (!Page.IsPostBack)
        {
            OleDbConnection MyConnection = null;
            DataSet DtSet = null;
            OleDbDataAdapter MyCommand = null;
            MyConnection = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" + path + "';Extended Properties=Excel 12.0;");
            MyConnection.Open();
            MyCommand = new OleDbDataAdapter("select Sname from [Sheet1$]", MyConnection);
            DtSet = new System.Data.DataSet();
            MyCommand.Fill(DtSet, "[Sheet1$]");
            DropDownList2.DataSource = DtSet;
            DropDownList2.DataTextField = "Sname";
            DropDownList2.DataValueField = "Sname";
            DropDownList2.DataBind();
            MyConnection.Close();
        }
    }
    protected void Unnamed1_Click(object sender, EventArgs e)
    {
        try
        {
            string excelconstr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" + path + "';Extended Properties=Excel 12.0;";
            OleDbConnection excelcon = new OleDbConnection(excelconstr);
            OleDbCommand cmd = new OleDbCommand("Select * from [Sheet1$] where class='" + DropDownList1.Text + "' and Sname='" + DropDownList2.Text + "'", excelcon);
            excelcon.Open();
            OleDbDataAdapter da = new OleDbDataAdapter(cmd);
            da.Fill(dt);
            gridview.DataSource = dt;
            gridview.DataBind();
            excelcon.Close();
        }
        catch (Exception ex)
        {
        }
    }
}