Embodiments of this application provide a QoS flow processing method and device, and a communications system. A first access network device sends a message used for a service transfer request to a second access network device, and the message used for the service transfer request includes configuration information of a QoS flow in the first access network device, so that the second access network device can configure a mapping relationship from the QoS flow to a DRB of the second access network device for UE based on the configuration information, and accept the QoS flow of the UE. Therefore, in a service transfer process, a reliable QoS service can be provided for a user, and continuity of a user service can be ensured.