The illumination analysis algorithm at mid-low latitudes is improved. Taking Aristarchus plateau (AP) as an example,the high resolution and high accuracy LOLA data from the LRO satellite and DE/LE430 lunar planetary ephemeris are used to quantitatively calculate and analyze the illumination characteristics of AP based on the Moon's libration model. The results show that the illumination rates of AP area are all over 0.35,and the illumination condition of flat area is good. The illumination rates vary greatly in different regions because of the influence of terrain. The maximum illumination rate is higher than the minimum above 30%. Considering the typical long term libration effects,the results of 18.6 years show that the change of illumination rate is small and stable,which is an important reference for the research on the evolution of the lunar surface.