This application discloses a PDU session establishment method and apparatus. The method includes: receiving, by a terminal device in a process of establishing a PDN connection in a first system, an access type that is sent by a core network device and that corresponds to the PDN connection in a second system; and when the terminal device moves to the second system, establishing, by the terminal device, a PDU session in the second system via an access network indicated by the access type, where the PDU session is associated with the PDN connection. Implementation of the present invention can increase a success rate of establishing a PDU session.