With the rapid development of inter-satellite communication systems, the requirements for data transmission accuracy are constantly increasing. As the core component, the spectral characteristics and surface shape accuracy of the beam splitter directly affect the transmission accuracy of the whole system. According to the interference theory of thin film, Ta₂O₅ and SiO₂ were selected as the high and low refractive index film materials for the design of the film system, and electron beam evaporation was used to prepare a high-precision beam splitter on a quartz substrate. At the same time, a surface shape correction model was established based on the principle of film stress compensation to control the surface shape. Through the detection of a spectral analyzer, it can be seen that the transmittance of beam splitter is greater than 98% at 1563 nm and the reflectance is greater than 99% at 1540 nm within the incidence range of 21.5° to 23.5°. The surface shape was measured by laser interferometer, it can be seen that the reflective surface shape accuracy RMS is corrected from λ/10 to λ/90 (λ=632.8 nm), and the transmissive optical surface shape accuracy RMS is λ/90.