问题是$content 是WordPress中的保留变量，必须使用其他名称。这里，我用过$pre_content:

<?php
/**
 * Plugin Name: T5 Editor content by request
 * Description: Default text for post content from GET variable <code>pre_content</code>.
 * Author:      Fuxia Scholz
 * Version:     2012.06.30
 */

/*
 * See wp-admin/includes/post.php function get_default_post_to_edit()
 * There are also the filters \'default_title\' and \'default_excerpt\'
 */
add_filter( \'default_content\', \'t5_content_by_request\', 10, 2 );

/**
 * Fills the default content for post type \'post\' if it is not empty.
 *
 * @param string $content
 * @param object $post
 * @return string
 */
function t5_content_by_request( $content, $post )
{
    if ( ! empty ( $_GET[\'pre_content\'] )
        and current_user_can( \'edit_post\', $post->ID )
        and \'\' === $content
    )
    {
        return $_GET[\'pre_content\'];
    }

    return $content;
}