A method for adjusting a service priority of a user, comprising: sending, by an Application Function, AF, service priority change information of User Equipment, UE, to a Policy Control Functionality, PCF, wherein the UE has registered with a network and activated a Packet Data Unit Session, PDU Session, and a network slice identifier, S-NSSAI, registered by the UE in the network is a first S-NSSAI, and a Network Slice Instance, NSI, corresponding to the first S-NSSAI is an NSI corresponding to a normal service priority user; notifying, by the PCF, a Session Management function, SMF, corresponding to the activated PDU Session to deactivate the PDU Session activated by the UE; deactivating, by the SMF corresponding to the activated PDU Session, the PDU Session activated by the UE, and notifying, by the SMF corresponding to the activated PDU Session, the UE to reestablish a PDU Session; receiving, by an Access and Mobility Management function, AMF, a PDU Session establishment request sent by the UE, wherein the PDU Session establishment request carries the first S-NSSAI; sending, by the AMF, a service authorization request message to the PCF, wherein the service authorization request message comprises an identifier of the UE and the first S-NSSAI; modifying, by the PCF, the first S-NSSAI into a changed S-NSSAI corresponding to the service priority change information according to the service priority change information of the UE; sending, by the PCF, a service authorization response message to the AMF, wherein the service authorization response message comprises the changed S-NSSAI; sending, by the AMF, a user slice information acquisition request message to a Network Slice Selection Function, NSSF, wherein the user slice information acquisition request message comprises the changed S-NSSAI; sending, by the NSSF, a user slice information acquisition response message to the AMF, wherein the user slice information acquisition response message carries NSI information corresponding to the changed S-NSSAI; selecting, by the AMF, an SMF corresponding to an NSI corresponding to the changed S-NSSAI according to the changed S-NSSAI, the NSI information corresponding to the changed S-NSSAI and a data network name, DNN; sending, by the AMF, a create session context request message to the SMF corresponding to the NSI corresponding to the changed S-NSSAI, wherein the create session context request message carries the changed S-NSSAI; sending, by the SMF corresponding to the NSI corresponding to the changed S-NSSAI, a create session context response message to the AMF; and establishing, by the SMF corresponding to the NSI corresponding to the changed S-NSSAI, and the AMF, a new PDU Session for the UE, wherein an S-NSSAI of the new PDU Session is the changed S-NSSAI. sending, by an Application Function, AF, service priority change information of User Equipment, UE, to a Policy Control Functionality, PCF, wherein the UE has registered with a network and activated a Packet Data Unit Session, PDU Session, and a network slice identifier, S-NSSAI, registered by the UE in the network is a first S-NSSAI, and a Network Slice Instance, NSI, corresponding to the first S-NSSAI is an NSI corresponding to a normal service priority user; notifying, by the PCF, a Session Management function, SMF, corresponding to the activated PDU Session to deactivate the PDU Session activated by the UE; deactivating, by the SMF corresponding to the activated PDU Session, the PDU Session activated by the UE, and notifying, by the SMF corresponding to the activated PDU Session, the UE to reestablish a PDU Session; receiving, by an Access and Mobility Management function, AMF, a PDU Session establishment request sent by the UE, wherein the PDU Session establishment request carries the first S-NSSAI; sending, by the AMF, a service authorization request message to the PCF, wherein the service authorization request message comprises an identifier of the UE and the first S-NSSAI; modifying, by the PCF, the first S-NSSAI into a changed S-NSSAI corresponding to the service priority change information according to the service priority change information of the UE; sending, by the PCF, a service authorization response message to the AMF, wherein the service authorization response message comprises the changed S-NSSAI; sending, by the AMF, a user slice information acquisition request message to a Network Slice Selection Function, NSSF, wherein the user slice information acquisition request message comprises the changed S-NSSAI; sending, by the NSSF, a user slice information acquisition response message to the AMF, wherein the user slice information acquisition response message carries NSI information corresponding to the changed S-NSSAI; selecting, by the AMF, an SMF corresponding to an NSI corresponding to the changed S-NSSAI according to the changed S-NSSAI, the NSI information corresponding to the changed S-NSSAI and a data network name, DNN; sending, by the AMF, a create session context request message to the SMF corresponding to the NSI corresponding to the changed S-NSSAI, wherein the create session context request message carries the changed S-NSSAI; sending, by the SMF corresponding to the NSI corresponding to the changed S-NSSAI, a create session context response message to the AMF; and establishing, by the SMF corresponding to the NSI corresponding to the changed S-NSSAI, and the AMF, a new PDU Session for the UE, wherein an S-NSSAI of the new PDU Session is the changed S-NSSAI.