Embodiments of this application provide a method for selecting an access network type, a device, and a system, to flexibly select an access network type. An example method includes: determining, by a policy control function PCF entity, that a network status of a first network does not meet a preset condition, where the first network is a network currently accessed by a terminal; and sending, by the PCF entity, an access network type corresponding to a second network to the terminal, where the access network type corresponding to the second network is used to instruct the terminal to redirect a session of the terminal to the second network, and the second network is a network other than the first network.