The present disclosure relates to dual connectivity methods. In one example method, a first access network device sends a request message to a second access network device, where the request message is used to request the second access network device to serve as a secondary access network device of a terminal served by the first access network device. Then, the first access network device receives an acknowledgment message from the second access network device, where the acknowledgment message is used to acknowledge to the first access network device that the second access network device agrees to serve as the secondary access network device of the terminal.