Abstract: The three-dimensional contour of the weld surface is an important index to evaluate the quality of the weld. In response to the problem that the measurement speed and accuracy cannot be balanced when the weld is measured by the commonly used line structured light scanning, a weld three-dimensional profile measurement system based on the surface structured light grating projection is designed and built. Firstly, the grating fringe is projected onto the weld through a digital light processing(DLP) projector, and the camera acquires the deformation modulation fringe. The phase of the deformed grating fringe is accurately calculated and unwrapped by using the four-step phase-shifting method combined with the multi-frequency heterodyne time-domain phase-resolving algorithm. Then, using a planar target combined with a high precision moving platform to obtain space coordinate data to calibrate the model parameters. The calibration method has high precision, strong operability and stable structure. Finally, the spatial phase mapping model is used to convert the phase information of the weld to the height information, and the measurement of the three-dimensional profile of the weld is realized. The test results show that this measurement method can well represent the detailed information of the weld, the measurement results are accurate, and the measurement accuracy can reach 0.096 8 mm, which can provide reliable data for the appearance inspection and evaluation of the post-weld.