This application provides communication methods, devices, and systems for improving communication efficiency. One communication method includes: receiving, by a target access network device and from a source access network device, a handover request message sent by a source access network device, wherein the handover request message is used to for requesting to hand over a terminal device from the source access network device to the target access network device; and obtaining, by the target access network device, network slice selection assistance information supported by the terminal device, wherein the network slice selection assistance information supported by the terminal device is used to indicates a network slice supported by the terminal device.