To solve the problem of measurement for welding deformation of sheet metal, a non-contact three-dimension optical method is proposed. Firstly, photos of moving objects from different observation points are taken by two high-resolution and high-speed digital cameras simultaneously. Secondly, the three-dimensional coordinates of targets are calculated by three-dimensional reconstruction technique including collinear equation, photo orientation based on the coplanar equation, direct linear transform, epipolar geometric constraint and bundle adjustment method. Finally, the deformations at different moments are associated with points of the same name; the deformation of the observation points is calculated and the real time deformation curves are sketched. Compared with the traditional methods, this method is not subjected to the high temperature and strong interference and has the advantages of real-time, high efficiency and high precision. The application in the measurement for welding deformation of sheet materials is satisfying.