Spare parts inventory is one of the most important contents in supportability analysis of aircrafts. Considering that scrap of spare parts was not taken into account in traditional analysis methods, an optimized model of resupply process was built aiming at maximizing the availability of spare parts. During such procedure, the initial supply and resupply are analyzed considering spare parts scrap and cost restrictions. It is assumed that once the scrap of spare parts exists, extra parts will be purchased immediately in the strategy of the analysis model. We obtained the solution method of top limit to availability at the end of each year. And relations among spare parts shortage costs, procurement costs and demand costs in queuing process are explicated in a formulation. Then the model is solved with an iterative algorithm. The optimized model is proved to be rational and validated by a comparison of numerical examples.