For part manufactures, there is one way to gain more profit is efficient controlling cost. To reduce cost, we cited the concept of buffer inventory to decouple the stage failure loss, avoid infra a work schedule, and remain a good will. Therefore, In this paper we concern an example of aero gear bearing manufacturing procedure. Also, we consider mathematical model which had proved as a convex function and it constrain by holding cost, shortage cost, storage cost for finished goods, and supplement cost. To find the system operation realistically, we derived some expressions of special repair time for stage failure-including constant, exponential, and earlang distribution. Due to the computational process is so tedious that we made a program with C language to eliminate the actions. By its execution, the rapid and convenient decision environment can be obtained.