A session establishment method includes receiving, by a mobility management function AMF entity, a first message sent by user equipment UE, where the first message carries identifier information, the identifier information is used to instruct the AMF entity to send the first message to a session management function SMF entity, and the first message is used to instruct the SMF entity to re-establish a session with the UE based on the identifier information by using a first user plane function UPF entity; and sending, by the AMF entity based on the identifier information, the first message to the SMF entity associated with the identifier information.