Abstract: In three-dimensional measurement system based on structured light, the grating fringe cycle is broadened on the reference surface with the reason of the oblique-angle, which brings errors to the measurement and reduces the accuracy. At the same time, because of large objects' geometry and morphology and other factors, as well as the limit of the intersecting axis projection system, the single shape measuring range is limited. It is difficult to measure large objects' complete shape in one time. And when measuring large objects, camera lens' nonlinear distortion also affects the measurement accuracy. According to the periodic pattern of grating stripes on the reference plane, a well-fitted, convenient and quick stripe cycle correction method was proposed. Based on the cycle correction method, a theoretical model of four-step phase shift method was put up, and then a theoretical model of time phase unwrapping based on fringe period correction was proposed. After that, the lens distortion correction model was used to improve the measurement accuracy. With the mark points pasted on the surface of objects, the three-dimensional coordinates of them were got, as well as the transformation matrix by using the singular value decomposition (SVD) and Levenberg-Marquardt (L-M) optimization algorithm, and three-dimensional image mosaic was realized under the global coordinate system. Finally, the linear weighting algorithm was used to realize the image fusion of overlapping areas. Experimental results show that the registration errors in x, y, z axes are 0.14 mm, 0.16 mm, and 0.19 mm respectively, which all meet the requirements.