Abstract: It has been proved that backscatter can be significantly reduced under water detection when laser source was modulated to be of narrower pulse at the emitter and echo was detected by narrow-band filter at the receiver. In practical applications, filter bandwidth is the key parameter for suppression of backscatter when modulation frequency has been determined. Based on previous study on seawater parameters and pulse frequency expanding characteristics, an ocean modulated lidar semi-physical simulation platform was established to study filter bandwidth. It is concluded that target contrast will firstly increase and then decline slowly with the increase of filter bandwidth. By comparing the experimental results, a method of filter bandwidth design was presented.