Thermal deformation of welding structure is inevitable in welding process. The deformation will not only change the appearance, shape and geometry size of the welding structure, reduce assembly quality but also may reduce the bearing capacity. On this basis, a welding deformation measurement based on visual method was proposed for the problem of the thermal deformation measurement in welding process. Theoretical calculations were carried out and an image processing and measurement algorithm based on MATLAB was also put forward. Then welding deformation measurement experiment was carried out and the results show that the welding deformation obtained by actual measurement is consistent with the theoretical analysis, proving the feasibility of welding deformation measurement based on vision. The welding deformation measurement based on visual method lays a foundation for automatic measurement of welding deformation.