A network slice instance management method for associating at least two network slice instance subnets to constitute a to-be-created network slice instance, comprising: sending, by a network manager, a first configuration request to a first element manager, wherein the first configuration request is used to configure a first network slice instance subnet based on a second network slice instance subnet and a requirement of a to-be-created network slice instance, and wherein the first configuration request comprises: description information of the second network slice instance subnet, description information of the to-be-created network slice instance, and configuration description information of the first network slice instance subnet; receiving, by the network manager, a configuration response message sent by the first element manager, wherein the configuration response message is used to indicate, to the network manager, that the first element manager completes configuration of the first network slice instance subnet; sending, by the network manager, an association request to a second element manager, wherein the association request is used to request the second element manager to associate with the second network slice instance subnet, and wherein the association request comprises the description information of the to-be-created network slice instance; and receiving, by the network manager, an association response message sent by the second element manager, wherein the association response message is used to indicate that the association of the second network slice instance subnet is completed and that the second network slice instance subnet can serve the to-be-created network slice instance. sending, by a network manager, a first configuration request to a first element manager, wherein the first configuration request is used to configure a first network slice instance subnet based on a second network slice instance subnet and a requirement of a to-be-created network slice instance, and wherein the first configuration request comprises: description information of the second network slice instance subnet, description information of the to-be-created network slice instance, and configuration description information of the first network slice instance subnet; receiving, by the network manager, a configuration response message sent by the first element manager, wherein the configuration response message is used to indicate, to the network manager, that the first element manager completes configuration of the first network slice instance subnet; sending, by the network manager, an association request to a second element manager, wherein the association request is used to request the second element manager to associate with the second network slice instance subnet, and wherein the association request comprises the description information of the to-be-created network slice instance; and receiving, by the network manager, an association response message sent by the second element manager, wherein the association response message is used to indicate that the association of the second network slice instance subnet is completed and that the second network slice instance subnet can serve the to-be-created network slice instance.