A session activation method, device, and system, and relate to the field of the communications technologies, to resolve an existing problem of relatively high signaling overheads during PDU session activation. The method includes: receiving, by a control plane node, indication information from an AMF node, where the indication information is used to indicate that the AMF node receives a service request message sent by a terminal device; and sending, by the control plane node, an identifier of a to-be-activated PDU session of the terminal device to an SMF node or the AMF node based on the indication information.