php对xml的操作十分简单，

$url = 'http://api.map.baidu.com/telematics/v3/weather?location=北京&output=xml&ak=gfPnxaaiPyNIhM7c3eZ1kmEL';
$xml = simplexml_load_file($url);

echo $city = $xml->xpath('//currentCity')[0];
foreach($xml->xpath('//weather_data') as $r) {
  $date = (array)$r->date;
  $dayPictureUrl = (array)$r->dayPictureUrl;
}
var_dump($city, $date, $dayPictureUrl);

北京object(SimpleXMLElement)#2 (0) {<br />}<br />array(4) {<br />  [0]=><br />  string(30) "周五(今天, 实时：24℃)"<br />  [1]=><br />  string(6) "周六"<br />  [2]=><br />  string(6) "周日"<br />  [3]=><br />  string(6) "周一"<br />}<br />array(4) {<br />  [0]=><br />  string(57) "http://api.map.baidu.com/images/weather/day/leizhenyu.png"<br />  [1]=><br />  string(51) "http://api.map.baidu.com/images/weather/day/yin.png"<br />  [2]=><br />  string(52) "http://api.map.baidu.com/images/weather/day/qing.png"<br />  [3]=><br />  string(52) "http://api.map.baidu.com/images/weather/day/qing.png"<br />}<br /><br />