Abstract: In order to accurately measure the three-dimensional surface shape of object, the influence of sampling on it was studied. Firstly, on the basis of deriving spectra expressions through Fourier transform, the generation of CCD pixels was analyzed and its expression was given. Then, basing on the discrete expression of deformation fringes obtained after sampling, its Fourier spectrum expression was derived, resulting in an infinitely repeated "spectra island" in the frequency domain. Finally, on the basis of using a low-pass filter to remove high-order harmonic components and retaining only one fundamental frequency component, the signal strength is reconstructed by inverse Fourier transform. A method of reducing the sampling interval, i.e. reducing the number of sampling points per fringe, was proposed to increase the ratio between the sampling frequency and the fundamental frequency of the grating, so as to more accurately reconstruct the object surface shape under the condition of