Embodiments of the present disclosure provide a session establishment method and system, and a device, to meet a low-latency requirement of group communication. The method includes: obtaining, by a mobility management entity, group identification information of a group to which a terminal belongs; determining, by the mobility management entity based on the group identification information, a session management entity that serves the group to which the terminal belongs; and sending, by the mobility management entity, the group identification information to the session management entity, where the group identification information is used to determine a user plane function entity that serves the group to which the terminal belongs.