Aiming at the problems of phase error and reduced reconstruction accuracy caused by grating deformation caused by strong surface reflection in the process of structured light 3D reconstruction, a reconstruction method based on local grating completion is proposed. Firstly, the reflection factors that cause the missing phenomenon of the 3D reconstructed point cloud model, such as the material properties of the measured object and the angle of specular reflection, are analyzed. Secondly, before the phase unwrapping, the local grating complement method is introduced to complete the missing part of the grating in the reflective area, and the phase unwrapping accuracy is improved based on the phase shift method and the complementary Gray code reconstruction method. Finally, by building a monocular structured light 3D reconstruction system, the 3D reconstruction of the reflective rectangular aluminum alloy plate with a flatness error within 0.5 mm is carried out. Experiments show that the improved method proposed in this paper can effectively complement the reconstruction loss caused by the reflection on the surface of the object, and its phase decoding information is more complete. Compared with the traditional method, the reconstruction rate is increased by 25%, and the flatness error rate is reduced by 28.2%.