A data forwarding method for interworking between a first network and a second network, the first network being a 4G network and the second network being a 5G network, the method comprising: receiving, by a session management function network element from an access and mobility management function network element, information about a first bearer in the first network, wherein the session management function network element integrates a packet data network gateway-control plane in the first network and a session management function in the second network, and the access and mobility management function network element is in the second network, said method being characterized by; determining, by the session management function network element, a first flow in the second network based on the information about the first bearer and association information, the first flow is a flow for data forwarding, wherein the association information indicates an association between the first flow and the first bearer; and sending, by the session management function network element to an access network device in the second network via the access and mobility management function network element, flow information of the first flow and forwarding information, wherein the flow information indicates the first flow, and the forwarding information is used by the access network device to identify a user plane function network element to which to forward the first flow, wherein the user plane function network element integrates a user plane function in the second network and a packet data network gateway-user plane in the first network for forwarding the first flow to a tunnel corresponding to the first bearer. receiving, by a session management function network element from an access and mobility management function network element, information about a first bearer in the first network, wherein the session management function network element integrates a packet data network gateway-control plane in the first network and a session management function in the second network, and the access and mobility management function network element is in the second network, said method being characterized by; determining, by the session management function network element, a first flow in the second network based on the information about the first bearer and association information, the first flow is a flow for data forwarding, wherein the association information indicates an association between the first flow and the first bearer; and sending, by the session management function network element to an access network device in the second network via the access and mobility management function network element, flow information of the first flow and forwarding information, wherein the flow information indicates the first flow, and the forwarding information is used by the access network device to identify a user plane function network element to which to forward the first flow, wherein the user plane function network element integrates a user plane function in the second network and a packet data network gateway-user plane in the first network for forwarding the first flow to a tunnel corresponding to the first bearer.