Laser beam measurement using point diffraction interferometer (PDI) is studied by modeling and the factors that influence the measurement accuracy are investigated. First, zernike polynomial is used to fit aberrated wavefront and the behavior of pinholes diffraction with different aberrated wavefront is analysed. The following essential work on the PDI sensor is to get balance between intensity of the spherical reference wave and test wave. Then the optimum parameters for the model are obtained: wavelength of laser is 1 024 nm; pinholes diameter is 2 μm; size of the focus spot is 20 μm; if gold (Au) is chosen as layer on film, its thickness should be 0.05 μm. The optimization results are only suited to the current PDI system, but the method presented is applicable to other configurations of high-accuracy PDI design.