如果您只需要第一个源标记， preg_match 应该代替 preg_match_all ，这对你有用吗？

If you only need the first source tag, preg_match should do instead of preg_match_all, does this work for you?

<?php
    $texthtml = 'Who is Sara Bareilles on Sing Off<br>
    <img alt="Sara" title="Sara" src="475993565.jpg"/><br>
    <img alt="Sara" title="Sara two" src="475993434343434.jpg"/><br>';
    preg_match('/<img.+src=[\'"](?P<src>.+?)[\'"].*>/i', $texthtml, $image);
    echo $image['src'];
?>