The defocused projection of binary fringe overcomes the nonlinear effect of fringe projection on 3D shape measurement， and effectively suppresses the error caused by Gamma effect of the used projector. Multi-frequency binary defocused fringe projection combined with temporal phase unwrapping is a common 3D shape measurement method for complex objects. In its application， it is necessary to ensure that multiple frequency binary fringes can get approximately the same sinusoidal quality， and the defocusing amounts of different frequency fringes are different， which is not conducive to its wide use. In this paper， the relationship between the defocused amount and the sinusoidal quality of the fringe with different binarization methods is analyzed， and a method of 3D shape measurement is proposed by using different binarization methods with the same fixed defocusing amount while projecting the different frequency fringes. The comparison， simulation and experimental results of the combined binary fringe method in this paper and the single frequency binary fringe method show that the combined binary fringe method proposed in this paper has higher accuracy and the defocusing amount of the fringe at different frequencies is fixed in practice， which is convenient and easy to operate.