There are problems in the previous system reliability optimization study because of system cost only including system price and without considering the system operation cost during the life cycles. We employ a simple calculation method of the spare parts’cost based on the estimation for spare parts demand during the whole life cycle， in the condition of two kinds of nonlinear reliability-price function， system composition units being not repaired and units’life time obeying exponential distribution， research system reliability allocation optimization as the goal of minimizing the sum of system price and spare parts cost. The simulation results show that the method is simple， convenient and feasible， and can effectively avoid over optimization when only pursuing the lowest system price at the expense of the whole life cycle cost. The system reliability optimization scheme， which based on the spare parts’cost of life cycle， can efficaciously reduce system operation cost during the life cycles.