您可以为此创建一个小插件，下面是一个小示例，它将尝试根据excerpt 职位字段：

add_action(\'publish_post\', \'auto_featured_image_publish_post\');
function auto_featured_image_publish_post($post, $post_id) {

  // check if this post is saved for the first time
  if($post->post_date == $post->post_modified) {

    // we\'re using the excerpt field, change this to whatever field
    // you\'re using
    $post = get_post($post_id);
    $htmlURL = $post->post_excerpt;

    // try to load the webpage
    $doc = new DOMDocument();
    $doc->loadHTMLFile($htmlURL);

    // get all image tags
    $images = $doc->getElementsByTagName(\'img\');

    // set the first image as featured image for the post, note that
    // you will have to handle relative urls, in other words
    // if $imageURL isn\'t an absolute url you\'ll need to append the
    // value of $post->excerpt
    if(count($images)) {
      $imageURL = $images[0]->getAttribute(\'src\');

      // download image from url
      $tmp = download_url($imageURL);

      $file = array(
        \'name\' => basename($imageURL),
        \'tmp_name\' => $tmp
      );

      // create attachment from the uploaded image
      $attachment_id = media_handle_sideload( $file, $post_id );

      // set the featured image
      update_post_meta($post_id, \'_thumbnail_id\', $attachment_id);
    }
  }
}

上述方法应该可行，但您当然应该添加代码来处理各种错误，还可能添加代码来检查图像的尺寸和类型是否有效，缩放图像等等。