Quantum communication is to construct protocols and algorithms using the Heisenberg Uncertainty principle of quantum mechanics, the No-Cloning theorem of quantum states and quantum entanglement properties to realize confidential communication in the real sense. Quantum communication is mainly divided into two kinds of quantum invisible transmission and quantum key distribution, of which the quantum key distribution technology is the most mature development, has been verified by researchers in various countries, and realized engineering applications. Restricted by the curvature of the earth and the loss of optical fiber, the ground-based quantum communication method can not achieve a wide range of quantum communication network coverage, so people will focus on the satellite platform, through the establishment of a highly stable and low-loss quantum channel between the satellite platform and the optical ground station, it can realize the ultra-long-distance quantum key distribution. The reflection element is an important part of the quantum key distribution system, which has the roles of efficiently transmitting optical energy and folding the optical path. When light is incident obliquely to the reflection element, the effective refractive index of the membrane layer for the p-polarized component and the s-polarized component is different, which generates the polarization effect and phase difference, leading to an increase in the quantum bit error rate; and when the light passes through the reflection element with the surface shape error, the different optical ranges experienced by the reflection on the surface lead to the distortion of the phase such as the wavefront, which influences the quality of coherent mixing and the efficiency of the communication coupling. Therefore, in order to improve the communication quality and reduce the bit error rate, the reflection element is particularly important to reduce the phase difference and surface shape error under the premise of ensuring higher reflectivity. In this paper, a low-sensitivity film system structure is designed to realize the preparation of high surface shape phase modulation reflective elements by stress compensation and so on.Based on the basic theory of thin film design, the relationship equation of phase difference Δ with respect to the incident angle θ, refractive index n and film thickness d at the wavelength λ position of a single-layer film is deduced. According to the principle of equivalent layer, the multilayer dielectric film can be equivalent to a single-layer dielectric film, and the phase difference Δ of the multilayer film can be calculated by changing the number of layers of the film system and the thickness of the film layer to obtain different equivalent refractive indices and equivalent phase thicknesses, so as to realize the precise regulation of the phase difference; combined with the optimization methods of the Essential Macleod software, such as Optimac, Nonlinear Simplex, etc., the spectra and phase difference Δ are designed and optimized. The phase-regulated reflective elements with spectra and phase difference meeting the usage requirements were designed.Based on the sensitivity analysis method, the sensitivity of the film thickness to the phase difference is studied, and the analysis shows that the sensitivity of the first 32 layers of the film is low, and the sensitivity of the 33rd and 34th layers is very high, and then ±1% of the film thickness error is introduced to the 33rd and 34th layers, respectively, and the phase difference still meets the requirements, which determines the feasibility of the design of the film system preparation.Film preparation using electron beam ion-assisted deposition method, the test can be obtained reflective element at 45° incidence, 632.8 nm ± 5 nm band reflectivity of 87.92%, 1 540 nm band p-reflectivity is 99.73%, s-reflectivity is 99.80%, the phase difference of 0.16°, 1 563 nm band p-reflectivity 99.74%, s-reflectivity 99.78%, phase difference of 0.16°, 1 563 nm band p-reflectivity 99.74%, s-reflectivity 99.78%, phase difference of 0.16°, the reflection element in the 45° incident. 99.74% p-reflectivity, 99.78% s-reflectivity, and 0.88° phase difference at 1 563 nm, which meets the spectral and phase difference requirements.Based on the stress balancing method, the same stress film layer is deposited on the back side to balance the stress of the front surface layer, which can realize the correction of the surface shape without affecting the spectra and phase difference of the deposited phase modulation reflective film. Combined with the SiO₂ deposition experiment, the mathematical model of the change of reflective surface shape and the thickness of SiO₂ deposition is established by linear fitting, and the thickness of SiO₂ deposited on the backside of the reflective element is calculated for the optimal reflective surface shape, and the RMS of reflective surface shape error is corrected to 0.004 94 λ by depositing 4 805 nm SiO₂ on the backside of the reflective element to realize the high-precision correction of the reflective surface shape. The calibration was realized with high precision reflective surface shape.According to the standard of GJB2485A-2019, the environmental adaptability test of the reflection was conducted, and the prepared reflection element passed the corresponding environmental adaptability test, which meets the requirements of the quantum key distribution system.However, there are still some problems in the development, and how to further reduce the sensitivity of the film layer to obtain a lower phase difference is the focus of the next step.