How to get services post data(json format) callback function?
Through comments, we determined the OP would like to alter the results
  of the user registration service resource...


To alter the results of user registration data, implement hook_services_request_postprocess_alter() in your custom module, for example:

/**
 * Implements hook_services_request_postprocess_alter().
 */
function my_module_services_request_postprocess_alter($controller, $args, &amp;$result) {
  if ($controller['callback'] == '_user_resource_register') {
    $result-&gt;foo = 'bar';
  }
}


This will allow the value of foo to be available to your application that is calling the user registration service resource.