A method for network slice selection policy updating performed by a device, comprising: Sending, by the device, in a registration request configured network slice selection assistance information, NSSAI, to an access and mobility management function, AMF, wherein the configured NSSAI comprises at least two configured slice identifiers including a first slice identifier and a second slice identifier; and Receiving, by the device, in a registration request response message allowed NSSAI and an updated network slice selection policy comprising indication information from the AMF, wherein the allowed NSSAI comprises at least one allowed slice identifier including a third slice identifier, wherein the indication information indicates a mapping between the at least two configured slice identifiers and the at least one allowed slice identifier; determining, based on a configured slice selection policy, that a first target application corresponds to the first slice identifier and a second target application corresponds to the second slice identifier, wherein the configured slice selection policy comprises a correspondence between the first target application and the first slice identifier and a correspondence between the second target application and the second slice identifier; determining, based on the indication information, that the first slice identifier and the second slice identifier correspond to the third slice identifier; transmitting data of the first target application and the second target application by using a session corresponding to the third slice identifier, wherein the transmitting data of the first target application and the second target application by using a session corresponding to the third slice identifier comprises: if the session corresponding to the third slice identifier has already been established for transmitting the data of the first target application, transmitting the data of the second target application by using the session corresponding to the third slice identifier; and storing, by the device, the allowed NSSAI and the indication information, and when the device moves out of a public land mobile network, PLMN, in which the device is currently located, deleting the stored NSSAI and indication information. Sending, by the device, in a registration request configured network slice selection assistance information, NSSAI, to an access and mobility management function, AMF, wherein the configured NSSAI comprises at least two configured slice identifiers including a first slice identifier and a second slice identifier; and Receiving, by the device, in a registration request response message allowed NSSAI and an updated network slice selection policy comprising indication information from the AMF, wherein the allowed NSSAI comprises at least one allowed slice identifier including a third slice identifier, wherein the indication information indicates a mapping between the at least two configured slice identifiers and the at least one allowed slice identifier; determining, based on a configured slice selection policy, that a first target application corresponds to the first slice identifier and a second target application corresponds to the second slice identifier, wherein the configured slice selection policy comprises a correspondence between the first target application and the first slice identifier and a correspondence between the second target application and the second slice identifier; determining, based on the indication information, that the first slice identifier and the second slice identifier correspond to the third slice identifier; transmitting data of the first target application and the second target application by using a session corresponding to the third slice identifier, wherein the transmitting data of the first target application and the second target application by using a session corresponding to the third slice identifier comprises: if the session corresponding to the third slice identifier has already been established for transmitting the data of the first target application, transmitting the data of the second target application by using the session corresponding to the third slice identifier; and storing, by the device, the allowed NSSAI and the indication information, and when the device moves out of a public land mobile network, PLMN, in which the device is currently located, deleting the stored NSSAI and indication information.