A software upgrade method, applied to an evolved packet core, EPC, system, wherein the EPC system comprises a system manager, a traffic decider, a first service server, and a second service server, and the first service server and the second service server are installed with service software of a first version; and the method comprises: controlling, by the system manager, the second service server to upgrade the installed service software from the first version to a second version and controlling the first service server to transfer, to the second service server, a service data flow that comprises a service flow identifier and that is on the first service server; receiving, by the traffic decider, a service request sent by a user equipment connected to the EPC system for the first time, and forwarding the service request to the second service server; allocating, by the second service server, the service flow identifier for the service request from the user equipment, the service flow identifier indicating whether the service data flow is to be forwarded to the first service server or the upgraded second service server; receiving, by the traffic decider, the service data flow sent by the user equipment, and forwarding the service data flow to the second service server based on the service flow identifier in the service data flow; and after the second service server becomes stable, controlling, by the system manager, the first service server to upgrade the installed service software from the first version to the second version; and characterized by before the forwarding the service request to the second service server: obtaining, by the traffic decider, attribute information of the user equipment; and when the attribute information indicates that the user equipment belongs to a preset user group, triggering execution of the step of forwarding the service request to the second service server; and when the attribute information indicates that the user equipment does not belong to the preset user group, forwarding the service request to the first service server. controlling, by the system manager, the second service server to upgrade the installed service software from the first version to a second version and controlling the first service server to transfer, to the second service server, a service data flow that comprises a service flow identifier and that is on the first service server; receiving, by the traffic decider, a service request sent by a user equipment connected to the EPC system for the first time, and forwarding the service request to the second service server; allocating, by the second service server, the service flow identifier for the service request from the user equipment, the service flow identifier indicating whether the service data flow is to be forwarded to the first service server or the upgraded second service server; receiving, by the traffic decider, the service data flow sent by the user equipment, and forwarding the service data flow to the second service server based on the service flow identifier in the service data flow; and after the second service server becomes stable, controlling, by the system manager, the first service server to upgrade the installed service software from the first version to the second version; and characterized by before the forwarding the service request to the second service server: obtaining, by the traffic decider, attribute information of the user equipment; and when the attribute information indicates that the user equipment belongs to a preset user group, triggering execution of the step of forwarding the service request to the second service server; and when the attribute information indicates that the user equipment does not belong to the preset user group, forwarding the service request to the first service server. obtaining, by the traffic decider, attribute information of the user equipment; and when the attribute information indicates that the user equipment belongs to a preset user group, triggering execution of the step of forwarding the service request to the second service server; and when the attribute information indicates that the user equipment does not belong to the preset user group, forwarding the service request to the first service server.