You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allfileusages gafcontinue="Huangf.jpg|85" />
  </query-continue>
  <query>
    <pages>
      <page pageid="56" ns="0" title="粒子物理详细介绍" />
      <page pageid="69" ns="0" title="粒子物理简介" />
      <page pageid="75" ns="2" title="用户:韩志龙" />
      <page pageid="77" ns="0" title="核子结构" />
      <page pageid="85" ns="0" title="济南大学粒子物理" />
    </pages>
  </query>
</api>