Based on the principle of measuring the 3D phase of deformation object with SPI,one step interference pattern method is proposed.And based on two-dimension FFT,a new method of measuring 3D phase of speckle interferogram is realized.Choosing Mach-Zehnder interference system and using CCD to receive the speckle pattern of the object before and after deformation respectively,the speckle pattern interference figure of a deformation object can be gotten by subtracting the two speckle pattern.Programming with MATLAB software to make Fast Fourier Transform of the speckle pattern interference figure,the 3D phase of the deformation object can be obtained.From the 3D phase distribution,3D object deformation can be detected and judged.That lays the foundation for further 3D stress analysis of the object.The experiment results show that the method is simple,fast and accurate.The precision can reach up to λ/10.