gallery是一个短代码，因此您需要解析该短代码以获取其中引用的图像：

function pull_image_from_gallery(){
  global $post;
  $pattern = get_shortcode_regex();
  preg_match_all( \'/\'. $pattern .\'/s\', $post->post_content, $matches );
  foreach ($matches[2] as $k=>$v) {
    if (\'gallery\' == $v) {
      $atts = shortcode_parse_atts($matches[3][$k]);
      if (!empty($atts[\'ids\'])) {
        $ids = explode(\',\',$atts[\'ids\']);
        $first = $ids[0];
        $image = wp_get_attachment_image_src( $atts[\'ids\'] );
        if (!empty($image)) {
          // do what you want with image
          return $image[0];
        }
      }
    }
  }
}

1. grab the regex that Core uses to extract shortcodesparse the attributesget the image （或尝试get_attachment_image_url() 如果更方便的话）