Gray codes are widely used in structured-light projection three-dimensional (3D) imaging because of good robustness and noise immunity. During the process of 3D measurement, due to the influence of equipment and other environmental noises, the gray-code decoding fringe-order edge and the truncated phase edge usually cannot be in an ideal alignment state, which causes the unwrapped phase to jump. In order to better avoid the level hopping error and make the error tolerance width of the edge hopping region larger, an inter-partition phase unwrapping method based on Gray codes was proposed. A Gray code image was added on the basis of the complementary Gray code, the additional code words were obtained by decoding all the Gray codes, and two auxiliary fringe orders were obtained by performing fringe order mapping with different displacements on the additional code words. Using all the fringe orders, the inter-partition phase unwrapping was performed on the truncated phase. When the error in the edge hopping region was greater than half a period, the unwrapping phase without hopping could still be obtained. The experimental results show that when the width of the edge error region is less than 3/4 of the stripe period width, the error caused by the level hopping can be effectively avoided.