The present invention discloses a method for protecting a data service in Metropolitan Area Transport Networks, a work path for services transport is established between a source node and a work destination node of the services in the Metropolitan Area Transport Network, and the method includes: setting a protection destination node using the nodes except the work destination node, and establishing a protection path between the source node and the protection destination node to protect the services of the work path; detecting by the source node the failure state of the links of the work path and the protection path, and the failure state of the nodes in the links; detecting by the work destination node and the protection destination node the failure state of the links connecting themselves with data devices, respectively, and notifying the source node when there is the failure state; switching the data services of the work path to the protection path after the source node detects the failure state of the link of the work path or the failure state of the nodes in the link, or receives a failure state notice from the work destination node.