'Private Sub ComboBox1_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles ComboBox1.SelectionChanged
    '    Dim cmd As New SqlClient.SqlCommand
    '    Dim tbl As New DataTable
    '    Dim da As New SqlClient.SqlDataAdapter
    '    Dim code As Integer
    '    Dim ds As New DataSet
    '    Dim sql_empid As String = cmbaaa.SelectedValue.ToString

    '    Try
    '        cn.Open()


    '        sql_empid = "select * from EmMaster where EmMaster_EmpName  Like %sql_empid"

    '        da = New SqlDataAdapter(sql_empid, cn)
    '        da.Fill(ds, "EmMaster")
    '        tbl = ds.Tables(0)

    '    Catch ex As Exception
    '        MessageBox.Show(ex.Message)
    '    Finally
    '        cn.Close()
    '    End Try
    'End Sub

hii frnds i work in vb.net windows apps now i use combobox to disply list of name but in combobox search the item when i type any letter Ex. i type A in combobox then dispaly all name in use A .
please solve my problem.

Thanks & Regards

Why is everything commented? When you declare sql_empid, you assign a value from another control, cmbaaa. Did you want to assign from Combo1 instead?

After opening the connection, you reassign sql_empid with a totally different string, referencing the initialized value. This is not generally considered good form; use seperate variables for the selected value and the SQL string, as this can make it harder to debug your code.

In SQL, to reference a field in a table, use a . to separate the table and field, not an underscore.

Pay attention to the details and try to follow best practices to avoid these kinds of problems.

Your codes are quite perfect.
your problem arises for the line Dim sql_empid As String = cmbaaa.SelectedValue.ToString.
When you are typing "A" sql_empid stores the value A and it displays all values which are using A.
So you can use

Dim sql_empid As String = cmbaaa.Items(cmbaaa.SelectedIndex)