function http_post_data($url, $data_string) {

        $ch = curl_init();
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
		curl_setopt($ch, CURLOPT_HTTPHEADER, array(
			'Content-Type: application/json; charset=utf-8',
			'Content-Length: ' . strlen($data_string))
		);
        ob_start();
        curl_exec($ch);
        $return_content = ob_get_contents();
        ob_end_clean();

        $return_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        return array($return_code, $return_content);
    }

$url  = "http://xx.xx.cn";
$data = json_encode(array('a'=>1, 'b'=>2)); 

list($return_code, $return_content) = http_post_data($url, $data);