To evaluate the system reliability and the constellation availability of remote sensing satellite, in this study, a novel single satellite availability modeling and analysis strategy using on-orbit backup and ground added launch backup is proposed. First, considering the characteristics of remote sensing satellites, the calculation formulas of constellation availability are given in detail. Then, the process of system reliability modeling is also illustrated step by step. Finally, an availability evaluation example of remote sensing satellite constellation is introduced to show the effectiveness of the proposed method.