A method of unwrapping phase by the spatial geometric constraints of the camera and projector is proposed. This method only needs to calibrate the structured light measurement system without conventional temporal or spatial phase unwrapping. The approximate height information of the object is obtained by projecting one-period fringes to determine virtual depth plane, and at the virtual plane z0min, the minimum absolute phase map is created according to the calibration parameters of the structured light system. And then the unwrapped phase of the object can be unwrapped pixel by pixel with reference to the minimum absolute phase map, by determining the number of fringe order. The proposed method has advantages of good robustness and low requirement for hardware, and it does not require any additional image acquisition and additional objects to obtain z0min, which can realize adaptive dynamic measurement. The experimental results show that under the same conditions, compared with the conventional temporal phase unwrapping method, the relative error of the proposed method is reduced by 14.33%, and the measurement method is simplified, which can effectively realize the three-dimensional shape measurement of objects.