Abstract: With respect to the situation that present Automatic Identification System (AIS) does not support the broadcast of BDS differential data, this paper studies differential message transmission and communication protocol of AIS, proposes a solution to broadcast BDS differential data through AIS. A test demonstration system is built to verify, verifies the feasibility of AIS-based BDS differential data broadcast system and result shows that the dynamic and static positioning accuracy of shipborne BeiDou AIS equipment can reach meter level. Propect of the application of AIS-based BDS differential data broadcast system in the maritime field is given in the end.