A packet transmission method, including receiving, by a session management function network element, first access network tunnel information and second access network tunnel information that correspond to a first service, and sending a downlink forwarding rule to a user plane function network element, where the downlink forwarding rule includes the first access network tunnel information and the second access network tunnel information, and the downlink forwarding rule indicates the user plane function network element to replicate a received downlink packet of the first service, and send downlink packets of the first service through two paths respectively corresponding to the first access network tunnel information and the second access network tunnel information.