According to target detection at sea, a method for target detection of ocean background based on polarization imagery fusion is presented. This method make use of the polarization information’s difference between the target and water, and good restrain of background noise. A group of image fusion rules are designed, and intensity of images, degree and phase of polarization images are fused by this rules. Finally, the results of fusion are tested by using the target detection method based on contour hierarchy tree. The experimental results show that the method can strengthen the target’s edge and texture features, enhance the contrast of target and background, which makes the target easier to be detected.