In phase measuring profilometry (PMP),a new calibration algorithm of phase shifting based on fast Fourier transform (FFT) is presented.With the help of computer emluator,it is found that a peak appear at double fundamental frequency spectrum of fringe pattern in Fourier domain,when there is a fixed error in each step of the moving of the project grating.Based on this,a new method of test error in Fourier domain is presented,and the error is minished by filter.