我不确定是否有用于此的本机函数，但一点正则表达式可能会有所帮助：

function open_links_in_new_tab($content){
    $pattern = \'/<a(.*?)?href=[\\\'"]?[\\\'"]?(.*?)?>/i\';

    $content = preg_replace_callback($pattern, function($m){
        $tpl = array_shift($m);
        $hrf = isset($m[1]) ? $m[1] : null;

        if ( preg_match(\'/target=[\\\'"]?(.*?)[\\\'"]?/i\', $tpl) ) {
            return $tpl;
        }

        if ( trim($hrf) && 0 === strpos($hrf, \'#\') ) {
            return $tpl; // anchor links
        }

        return preg_replace_callback(\'/href=/i\', function($m2){
            return sprintf(\'target="_blank" %s\', array_shift($m2));
        }, $tpl);

    }, $content);

    return $content;
}

add_filter(\'the_content\', \'open_links_in_new_tab\', 999);