add a “list” into add meta box : problem

You are missing the declaration of the HTML select tag which options are his children so just add something like this:

function myplugin_inner_custom_box() {
    // Use nonce for verification
    wp_nonce_field( plugin_basename( __FILE__ ), 'myplugin_noncename' );

    // The actual fields for data entry
    echo '<label for="myplugin_new_field">';
    _e("Description for this field", 'myplugin_textdomain' );
    echo '</label> ';
    echo '<input type="text" id="myplugin_new_field" name="myplugin_new_field"/>';

    //the actual select tag
    echo '<label for="my_list_field">';
    _e("Description for this field", 'myplugin_textdomain' );
    echo '</label> ';
    echo '<select name="my_list_field" id="my_list_field">';
    $s_query = new WP_Query( array(
    'suppress_filters' => false,
    'post_type' => 'movies'));
    while($s_query->have_posts()):$s_query->the_post();

        $sname = $post->post_title;
        $s_output2 ='';
        $s_output2 .= '<option value="'.$post->ID.'" >';
        $s_output2 .= $post->post_title;
        $s_output2 .= '</option>';
        echo $s_output2;

    endwhile ;
    echo '</select>';
    wp_reset_query();
}