$json_str = ‘{"thumb":"","photo":[{"url":"557a3d2184db0.png","alt":"SafeBoot\u6ce8\u518c\u8868"}]}‘; // json字符串
$obj = json_decode($json_str);
$photo = $obj->photo;
$url = $photo[0]->url; // echo url; //557a3d2184db0.png
原文：http://www.cnblogs.com/bushe/p/4571090.html