Satellite laser ranging (SLR) is a high-precision satellite orbit measurement method. Laser reflectors, as a key payload for SLR, have been used on many Earth orbit satellites and play an important role in fields such as astronomical geodynamics. In recent years, with the resurgence of the moon exploration craze, many countries have begun to try to carry laser reflectors on satellites in lunar orbit. For high-orbit satellites such as lunar orbit satellites, an array reflector composed of a large number of small-aperture corner reflectorsis usually used to ensure the success rate of ranging. However, due to the limitations of satellite resources, the weight and size of the payload are usually required to be as small as possible, so arrayed laser reflectors are no longer suitable. Single large-aperture laser reflectors are not only lightweight and small in size, but also have the advantage of concentrating reflected laser energy, making it possible for lunar orbit satellites to carry high-performance laser reflectors. However, the thermal environment in lunar orbit is complex and changeable, and large-aperture corner reflectors are significantly affected by temperature effects, which can lead to a decrease or instability in the reflector's reflective ability. Therefore, it is essential to conduct research on the thermal characteristics of large-aperture laser reflectors. A far-field diffraction pattern (FFDP) simulation model of the laser reflector was established. The simulation obtained the FFDP and optical scattering cross (OCS) of the laser reflector with three different apertures of 32, 38, 102 mm. The reflection capabilities of these three laser reflectors of different apertures were analyzed and compared. A thermal simulation model was established for the large-aperture lunar laser reflector in orbit, and the temperature conditions of the large-aperture laser reflector under different operating conditions were obtained. Based on the results of the thermal simulation, the FFDP and OCS of the large-aperture laser reflector under the influence of different temperature effects were experimentally tested, and the optical performance and in-orbit reflectivity of the large-aperture laser reflector affected by temperature effects were further analyzed.The FFDP of the 102 mm diameter laser reflector is more concentrated, and the peak light intensity is about two orders of magnitude higher than that of the 32 mm and 38 mm diameter laser reflectors (Fig.4). Similarly, the OCS value of the large-aperture laser reflector is also two orders of magnitude higher than that of the small-aperture laser reflector (Fig.4). According to the results of thermal simulation, the on-orbit temperature of the laser reflector ranges from -34.8 ℃ to 75.0 ℃, and the laser reflector shows the characteristics of low temperature at the bottom and high temperature at the tip, with a certain longitudinal temperature difference. The longitudinal temperature difference increases with the increase of light conditions. It is 0.9 ℃ in the absence of light, and can reach 6.1 ℃ under long-term sunlight irradiation (Fig.7, Tab.4). The FFDP and OCS were tested under different longitudinal temperature differences by heating the laser reflector. When the longitudinal temperature difference is below 1 ℃, the FFDP energy is concentrated and the reflector has good optical performance. After 1 ℃, the FFDP begins to disperse and the optical performance of the reflector gradually begins to decline (Fig.10). The OCS value gradually decreases with an increase in the longitudinal temperature difference (Fig.11). However, it is worth noting that different heating methods can lead to different rates of decrease in the OCS value.The large-aperture lunar laser reflector has an ideal reflective capacity. When the laser reflector is not exposed to sunlight, its longitudinal temperature difference is kept below 1 ℃, which is the best observation window.When the reflector is exposed to sunlight, the longitudinal temperature difference increases by more than 1 ℃, and the reflectivity is seriously affected, so observations are usually avoided during this period. Future research should focus on new materials and structural designs to enhance the stability and reflective capacity of large-aperture reflectors in extreme temperature environments. This will promote the development of deep space exploration and scientific research and help humanity gain a deeper understanding of the moon and its resources.