您可以将 XPath 与 predicate not(node()) 选择所有没有子节点的元素.

You can use XPath with the predicate not(node()) to select all elements that do not have child nodes.

<?php
$doc = new DOMDocument;
$doc->preserveWhiteSpace = false;
$doc->loadxml('<parentnode>
    <tag1>2</tag1>
    <tag2>4</tag2>
    <tag3></tag3>
    <tag2>4</tag2>
    <tag3></tag3>
    <tag2>4</tag2>
    <tag3></tag3>
</parentnode>');

$xpath = new DOMXPath($doc);

foreach( $xpath->query('//*[not(node())]') as $node ) {
    $node->parentNode->removeChild($node);
}

$doc->formatOutput = true;
echo $doc->savexml();

打印

<?xml version="1.0"?>
<parentnode>
  <tag1>2</tag1>
  <tag2>4</tag2>
  <tag2>4</tag2>
  <tag2>4</tag2>
</parentnode>