假设您的TinyMCE4容器的id为“tiny-mce-4”，您可以将此js添加到functions.php.

function toArray (collection) {
    return Array.prototype.slice.call(collection);
}

var imgs = toArray(document.querySelectorAll(\'#tiny-mce-4 img\'));


imgs.forEach(function(img){
    img.setAttribute(\'style\', img.getAttribute(\'style\').replace(/((height:).*?(px;))/g, \'max-width: 100%;\'));
});

<div id="tiny-mce-4">

  <img src="img1" style="height: 500px; width: 800px;" />
  <img src="img2" style="height: 500px; width: 800px;" />
  <img src="img3" style="height: 500px; width: 800px;" />
  <img src="img4" style="width: 800px;" />

</div>

  <img src="img5" style="height: 500px; width: 800px;" />