Abstract: In the space gravitational wave detection system, the accuracy of the complex amplitude field distribution simulation at the telescope exit pupil closely affects the accuracy of the interferometric measurement and impacts the effectiveness of TTL noise control analysis. Therefore, it is necessary to carry out the high-precision diffraction calculation for the field propagation. This paper demonstrates the necessity of the vectorial ray-based diffraction integral algorithm for simulation and illustrates the algorithm flow combining the telescope model. A computational model was established based on the algorithm. The telescope system parameters were substituted to verify the wavefront calculation accuracy, and the vectorial field simulation results were presented. Based on the system model, the effects of the input Gaussian field parameters and the complex refractive index on the output vectorial optical field characteristics are simulated.