In order to provide continuous and stable performance services for satellite constellation in a global or specific region, it is necessary to put forward new requirements for satellite constellation availability. This paper studies the changes of satellite constellation availability over time. Based on the METRIC (Multi-Echelon Technique for Recoverable Item Control) theory, the availability of satellite constellation and its influencing factors are analyzed. The calculation method of parameters related to the availability of the constellation is given based on these factors. That is, the average annual demand, expected demand and expected shortage of satellites of orbits and ground bases are considered in turn according to the replenishment mode of the constellation, and the availability calculation model of the inclined orbit satellite constellation is established and deduced in the implementation process. Finally, the calculation formula for the satellite availability of the whole constellation is obtained, and then applied in the actual case model. According to the failure efficiency corresponding to different satellite failure types, calculate the maximum population of faulty satellites that the system can bear within the availability requirements. Through comparison, it is further concluded that with the increase of satellite failure efficiency or the increase of the population of faulty satellite stars, the availability of constellation will also decline, and even the change of failure efficiency has a more significant impact.