In the three-dimensional measurement of structured light, the measurement structure only with a single projector is prone to occlusion and shadow in the measurement of complex objects and thus the integrity of measurement data is influenced. In contrast, the measurement structure with double projectors can broaden the imaging area and reduce the shadowing region, and thus the measurement efficiency is improved. However, it is still difficult to separate the original projection signals from the partially overlapping phase-shift gratings for this method. On the basis of the analysis of the conventional four-step phase-measuring method, a separation method of overlapping phase-shift gratings is proposed via the complementarity of gray scales, in which the invalid overlapping signals are effectively eliminated by adjusting the time and sequence of the projected phase-shift gratings while keeping the original measuring structure. As for the verification of the effectiveness of the above separation method, a measurement system is established to conduct the related experiments. The results show that the complementarity of gray scales can be used to realize the accurate separation of overlapping phase-shift grating signals, obtain the complete point cloud data, and improve the measurement speed.