The embodiments of present invention provide a mobile communications method, a device, and a system. The method is performed by an access network device, including: receiving, by using a terrestrial interface of a first network standard between an access network and a first core network, a first terrestrial interface message of the first network standard sent by the first core network; generating, according to an air interface protocol of an air interface of a second network standard between the access network and UE and the first terrestrial interface message, a first air interface message of the second network standard; and sending, by using the air interface of the second network standard, the first air interface message to the UE. The method implements direct communication between network devices of different standards in a mobile communications system, thereby decoupling an air interface from a terrestrial interface.