After self-study, I know how to get the url image in the comment with the following code, this code put in the functions.php file.
functions.php:

function get_attachment_url_image_comment($comment_id) {
    $meta_key = 'attachment_id';
    $attachment_id = get_comment_meta( $comment_id, $meta_key, true );
    $full_img_url = wp_get_attachment_image_url( $attachment_id, 'full' );
    return $full_img_url;
}

view:

<?php $comments = get_comments($param) ?>
<?php foreach($comments as $comment): ?>
   echo get_attachment_url_image_comment($comment->comment_ID);
<?php endforeach; ?>

It works fine!