In order to achieve three-dimension high-speed and large-scale measurement to underwater objects,an underwater line structured-light self-scan three-dimension measuring technology is presented. A galvanometer is adopted to reflect laser plane onto object′s surface. The laser plane intersects the surface of object and a light stripe which is photographed by a camera is formed. According to the position of each point of light stripe on image,the offset caused by refraction is calculated and compensated. Then utilizing the equation of laser plane in water,accurate 3D coordinates of detected points are accurately calculated out. Experimental results show that the model of underwater self-scan system and underwater three-dimension measurement method are feasible. The measurement precision in the space of depth of 0.5-1 m,measuring height of 0.5 m and measuring width of 0.6 m achieves 0.7 mm.