Based on the optical path of the Maher Zed interferometer,the optical phase control technique is used to generate the interference projection fringe for the measurement of optical topography.In order to study the effect of phase modulation error of optical phase control device on the quality of interference fringes,the model of the quality of interference fringes is established.The relationship between the refractive index,the flatness and the wavefront modulation is analyzed,and the effect of those on the quality of interference fringes is also analyzed.The simulation results show that the modulation error of the electro-optical crystal will affect the quality of the interference fringes.The distortion of the crystal refractive index under the ideal planeness can cause the distortion of the interference fringes.The discrete order number of the refractive index directly influences the higher harmonic components of the projection fringes,and even causes the serious distortion of the projected fringes;when the refractive index is ideal,the difference of the crystal planeness will cause the different distortions of the interference fringes.