I need some code sample, please contribute me some code.

I hope the following code snap will help you:(http://wordpress.org/support/topic/how-to-show-top-authors-with-avatar-and-count)

<?php
global $wpdb;
$top_authors = $wpdb->get_results("
    SELECT u.ID, count(post_author) as posts FROM {$wpdb->posts} as p
    LEFT JOIN {$wpdb->users} as u ON p.post_author = u.ID
    WHERE p.post_status = 'publish'
    AND p.post_type = 'post'
    GROUP by p.post_author
    ORDER by posts DESC
    LIMIT 0,10
");
if( !empty( $top_authors ) ) {
    echo '<ul>';
    foreach( $top_authors as $key => $author ) {
        echo '
        <li>
            <a href="' . get_author_posts_url( $author->ID ) . '">' . get_the_author_meta( 'user_nicename' , $author->ID ) . '</a>
            (' . $author->posts . ') ' . get_avatar( $author->ID , 4 ) . '
        </li>
        ';
    }
    echo '</ul>';
}
?>