$string = '<xml>

    <return_code><![CDATA[SUCCESS]]></return_code>

    <return_msg><![CDATA[OK]]></return_msg>

    <appid><![CDATA[wx2421b1c4370ec43b]]></appid>

    <mch_id><![CDATA[10000100]]></mch_id>

    <device_info><![CDATA[1000]]></device_info>

    <nonce_str><![CDATA[sthBJ9QyUG6vkrjJ]]></nonce_str>

    <sign><![CDATA[6277A96D7875D4FF23AA7B6A4C3046AB]]></sign>

    <result_code><![CDATA[FAIL]]></result_code>

    <err_code><![CDATA[PAYERROR]]></err_code>

    <err_code_des><![CDATA[支付错误]]></err_code_des>

</xml>';

$xml =(array)(simplexml_load_string($string,'SimpleXmlElement',LIBXML_NOCDATA));

print_r($xml);

//结果如下

C:\wamp\bin\php\php5.4.12\php.exe C:\wamp\www\pra\xml2arr.php

Array

(

    [return_code] => SUCCESS

    [return_msg] => OK

    [appid] => wx2421b1c4370ec43b

    [mch_id] => 10000100

    [device_info] => 1000

    [nonce_str] => sthBJ9QyUG6vkrjJ

    [sign] => 6277A96D7875D4FF23AA7B6A4C3046AB

    [result_code] => FAIL

    [err_code] => PAYERROR

    [err_code_des] => 支付错误

)

Process finished with exit code 0