Abstract: On the background of low-altitude radar seeker detecting the sea surface targets, this paper analyzes the effect of the multipath scattering and sea clutter on the detection performance of radar seeker. On the basis of modeling the target echo, specular reflection, diffuse reflection and the sea clutter, it gives the specular reflection signal, diffuse reflection signal and sea clutter radar seeker received under concrete circumstances by simulation. Then it analyzes the effect of the multipath scattering and sea clutter on the detection performance of radar seeker when detecting different size targets. Simulation results shows that sea clutter is the key factor affecting the detection performance of radar seeker when radar seeker detects the small target whose RCS is lower than 1 m2. While multipath effect is the key factor affecting the detection performance of radar seeker when radar seeker detects the target whose RCS is bigger than 10 m2. The detection performance of radar seeker is not affected when the radar seeker detects the target whose RCS is bigger than 104 m2.