Polarization detection method is used in underwater target image detection,which provides a new method for underwater targets detection in complicated ocean environment. The laser polarization detection principle is introduced,and a simple polarization detection system is constructed to detect different man-made targets. Experimental results show that different targets of different materials have different polarization properties,which is very useful for underwater targets detection and identification. An image processing method based on Matlab is proposed. Polarization images improve the definition and the contrast between targets and background. Therefore,man-made targets can be easily distinguished from natural background.