Absorption and scattering of seawater for light waves seriously restrict the performance of laser radar for underwater target detection. Quantitative analysis of laser backscattering generated by seawater shows that the laser echo signal is seriously affected by seawater backscattering. The ability of range-gated technology and intensity modulation technology to suppress backscattering of seawater was analyzed and compared. A chaotic pulse laser with high frequency intensity modulation was proposed for underwater target detection and the scheme was designed. Based on the study of the characteristics of backscattering light and echo signal with different backscattering intensity in time and frequency domain, the ability of chaotic pulse lidar to suppress backscattering from seawater was determined by using cross-correlation noise level algorithm. The theoretical analysis shows that the target signal can still be extracted when the backscattered light intensity is 36 times that of the chaotic pulse laser.