To meet the requirements that airline depresses initial spares cost and increases the airplane-s utilization, maximum marginal utility based optimal methods for initial spares scenario was presented. By the algorithm of Poisson distribution, items spare scenarios could be given only when the support probabilities were known. The defect of this method was that the spares scenarios may be not optimal. In order to solve this problem, the optimal model and implementing process of marginal analysis were presented, and then the spares- numbers of all parts in the item list were calculated at the same time. The initial spares scenario case was optimized by spare optimal software in the condition that either spares cost was invariable or operational availability was invariable. Cost-efficiency curves were drawn and datasheets of two optimal scenarios were got. The increase of operational availability and decrease of spares cost were discovered by comparison of data in the cost-efficiency curve. And so, the trend of spare number change was also seen by analysis of datasheets. The result shows that the optimal algorithm has wide application in initial spares scenario optimization of civil aviation.