Abstract: The rise of unmanned equipment poses major challenges to current maritime defense.Traditional radar has high cost and complex system,and Forward Scatter Radar(FSR)has the advantage of simple structure,low power consumption and low cost, The large range detection and monitoring of sea surface target can be realized through network . The wave fluctuation and multipath interference have great influence on the echo characteristics of the target .In this paper,the target signal model of FSR on sea wave is given first and then the signal model on multipath interference is given.,and the echo characteristics of the target in the two models are simulated and compares by Matlab,the conclusion is that multipath interference is the most important fator affecting the target echo signal in low wind speed sea wave.