Abstract: This paper proposes a new kind of maintenance model which characteristic is in the system level,incompletely maintenance and sequential maintenance.The model introduces age reduction factor measuring the maintenance effect and obtains the system reliability by the adjacency matrix method and the structural function matrix method.At the same time,the influence of the replacement of each component on the system reliability and total cost is taken account,and the formula for calculating the reliability and the total cost is derived.Then,using the NSGA-II method to make the multi-objective optimization of the model,obtaining the multi-objective maintenance plan about a system for the whole life of a nuclear power plant and making suggestions for maintenance decision making.Finally,an example is presented to verify the calculation steps,the economic analysis and multi-objective optimization of the maintenance program.