A communication method for a communication system comprising a first network, a second network, and a second terminal, wherein the first network comprises a first terminal, a first control plane network element, and a user plane network element; the second network comprises a second control plane network element; and the second terminal is accessible to the second network by using the first network, the method comprising: obtaining, by the first control plane network element, a quality of service parameter and/or a charging policy of a service flow in the first network, wherein the service flow is a service flow in which the second terminal communicates with the second network by using the first terminal and the user plane network element in the first network; sending, by the first control plane network element, the quality of service parameter and/or the charging policy of the service flow in the first network to the user plane network element and/or the first terminal; and wherein the sent quality of service parameter and/or the sent charging policy of the service flow in the first network is used for transmitting the service flow between the second terminal and the second network, and wherein the obtaining, by the first control plane network element, the quality of service parameter and/or the charging policy of the service flow in the first network comprises: obtaining, by the first control plane network element, a quality of service parameter and/or a charging policy of the service flow in the second network from the second control plane network element; and determining, by the first control plane network element, the quality of service parameter of the service flow in the first network based on the quality of service parameter of the service flow in the second network and/or determining the charging policy of the service flow in the first network according to the charging policy of the service flow in the second network. obtaining, by the first control plane network element, a quality of service parameter and/or a charging policy of a service flow in the first network, wherein the service flow is a service flow in which the second terminal communicates with the second network by using the first terminal and the user plane network element in the first network; sending, by the first control plane network element, the quality of service parameter and/or the charging policy of the service flow in the first network to the user plane network element and/or the first terminal; and wherein the sent quality of service parameter and/or the sent charging policy of the service flow in the first network is used for transmitting the service flow between the second terminal and the second network, and wherein the obtaining, by the first control plane network element, the quality of service parameter and/or the charging policy of the service flow in the first network comprises: obtaining, by the first control plane network element, a quality of service parameter and/or a charging policy of the service flow in the second network from the second control plane network element; and determining, by the first control plane network element, the quality of service parameter of the service flow in the first network based on the quality of service parameter of the service flow in the second network and/or determining the charging policy of the service flow in the first network according to the charging policy of the service flow in the second network. obtaining, by the first control plane network element, a quality of service parameter and/or a charging policy of the service flow in the second network from the second control plane network element; and determining, by the first control plane network element, the quality of service parameter of the service flow in the first network based on the quality of service parameter of the service flow in the second network and/or determining the charging policy of the service flow in the first network according to the charging policy of the service flow in the second network.