Provided are a data transmission method and apparatus. The method includes: detecting, by a source base station, that link quality of a connection with a terminal degrades; sending data unsuccessfully transmitted by a DU via a downlink data frame to a target base station through a CU, and transmitting the data unsuccessfully transmitted to the terminal through the target base station; or receiving, by the target base station, a link quality degradation message of an original base station so as to stop sending offload data to the source base station and transmitting the data unsuccessfully transmitted indicated by a maximum serial number of the data which has been transmitted continuously and successfully in the message to the terminal.