Embodiments of the present disclosure provide a session connection establishment method and system, and a related device. The method may include: receiving, by a first radio access network device, an initial attach request sent by a terminal device; sending, by the first radio access network device, the initial attach request to a first core network device; receiving, by the first radio access network device, an initial attach request feedback that is sent by the first core network device in response to the initial attach request, where the initial attach request feedback includes session identifiers of at least two user plane session connections, and sending, by the first radio access network device, session configuration information to the terminal device.