Abstract: To study the offshore ambient noise in the mid and low frequency band, an algorithm for calculating the contribution of ship noise to the offshore ambient noise is constructed, and the ship noise in a certain sea area is simulated by using the ship information and combining with the actual hydrological parameters. The ship information is obtained by accessing the ship automatic identification system (AIS) database. The ambient noise in the mid and low frequency band of 50~400 Hz is mainly concerned. The simulation results are compared with experimental data to verify the reliability of the algorithm, and the error analysis is made. By using this algorithm, the horizontal distribution of ship noise at the receiving point can be obtained, and the con-tribution of ship noise to offshore ambient noise can be preliminarily quantitatively analyzed.