In the light of the issue of storage level of aviation spares with different requirements, the optimal models of spares storage level based on the availability centered and the cost centered are established respectively according to the benefit optimal principle of military and economy. The inventory cost model is given, in which the purchasing cost is a master cost index. Assuming that the spares demand is a Poisson distribution with intensity λ, and the spares repair time is identical distribution with mean T. Then the availability model is given by Palm's theorem, in which the expected backorder is the scale index. And spares quantity is confirmed by iterative calculation, according to the marginal analysis method, in which the return value of marginal utility is the ratio of marginal increment and unit price for spares. Finally, it shows that the model and method are effective in balancing the relation between efficiency and cost through the analysis and comparison of particular cases.