A data transmission method and an apparatus, the method including sending, by an access network device, a paging message to a terminal device, where the paging message includes a first indication, receiving, by the access network device, a random access preamble from the terminal device, where the random access preamble corresponds to the first indication, and sending, by the access network device in response to the random access preamble, a response message to the terminal device, where the response message includes downlink data and one or more of a timing advance (TA), an uplink grant (UL-Grant), a temporary cell radio network temporary identity (TC-RNTI), a logical channel identifier (LCID), or a downlink assignment (DL-assignment).