A transmission control method applied when a packet data unit session has a plurality of paths corresponding to a plurality of anchor user plane function network elements, comprising: in a process of re-allocating for the packet data unit session a first intermediate user plane function network element to a second intermediate user plane function network element, sending, by a session management function network element, a respective session modification request of a plurality of session modification requests to each anchor user plane function network element of the plurality of anchor user plane function network elements, wherein each session modification request of the plurality of session modification requests comprises information about the second intermediate user plane function network element, the first intermediate user plane function network element connects to a source radio access network and connects to the plurality of anchor user plane function network elements, and the second intermediate user plane function network element connects to a target radio access network and connects to the plurality of anchor user plane function network elements; and indicating to, by the session management function network element, only a first anchor user plane function network element in the plurality of anchor user plane function network elements to send an end marker comprising: after the session management function network element sends the respective session modification request to each anchor user plane function network element other than the first anchor user plane function network element in the plurality of anchor user plane function network elements, indicating to, by the session management function network element, the first anchor user plane function network element to send the end marker, wherein the first anchor user plane function network element is the last anchor user plane function network element that updates path in the plurality of anchor user plane function network elements. in a process of re-allocating for the packet data unit session a first intermediate user plane function network element to a second intermediate user plane function network element, sending, by a session management function network element, a respective session modification request of a plurality of session modification requests to each anchor user plane function network element of the plurality of anchor user plane function network elements, wherein each session modification request of the plurality of session modification requests comprises information about the second intermediate user plane function network element, the first intermediate user plane function network element connects to a source radio access network and connects to the plurality of anchor user plane function network elements, and the second intermediate user plane function network element connects to a target radio access network and connects to the plurality of anchor user plane function network elements; and indicating to, by the session management function network element, only a first anchor user plane function network element in the plurality of anchor user plane function network elements to send an end marker comprising: after the session management function network element sends the respective session modification request to each anchor user plane function network element other than the first anchor user plane function network element in the plurality of anchor user plane function network elements, indicating to, by the session management function network element, the first anchor user plane function network element to send the end marker, wherein the first anchor user plane function network element is the last anchor user plane function network element that updates path in the plurality of anchor user plane function network elements.