Embodiments of this application provide a downlink data transmission method and apparatus. The method includes: receiving, by a user plane device, downlink data of a terminal, sending, by the user plane device, the downlink data by using a shared bearer to an access network device that is in a tracking area of the terminal, receiving, by the access network device, a context setup request message sent by a control plane device, setting up, by the access network device, a radio bearer between the access network device and the terminal based on the context setup request message, and sending, by the access network device, the downlink data to the terminal by using the radio bearer. In this way, a downlink data transmission delay is reduced and downlink data transmission efficiency is improved.