The 3D measurement method based on phase unwrapping of structured light is widely used because of its high accuracy. However, the phase will be folded when the phase exceeds 2π, so the traditional 3D reconstruction of structured light requires phase unwrapping. The unwrapping phase of phase measurement profilometry at discontinuous depth is complicated. When there is a large depth difference on the surface of the measured object or when multiple planes are measured, because the wrapping phase range is［0, 2π］, there is a problem of folding multiple 2π in the phase difference calculated at the discontinuity, resulting in unwrapping failure. Phase measurement profilometry can not accurately express the position information of the object at this time. A three-dimensional measurement method of structured light based on defocus unwrapping is proposed. The 24-step phase shift method is used to obtain the wrapping phase, and the number of wrapping phase 2π is determined by time defocusing method to assist the unwrapping calculation. A corresponding platform is built and experiments are carried out to verify the proposed method. Experiments show that the proposed method solves the problem that the phase measurement profilometry can not accurately express the position of the object when the depth drop is large. The method can be used to obtain the depth information and details of the scene with large depth drop.