The purpose of this study is to develop an evaluation method to optimize both cost and risk in maintenance strategy of BWR plant in long-term operation. Plant operation is simulated in a simplified model, and the condition of the components treated in the model are evaluated statistically with Monte Carlo simulation. While Probabilistic Safety Assessment(PSA) methods such as Fault Tree Analy sis(FTA), Event Tree Analysis(ETA), and Failure Mode and Effects Analysis(FMEA) are also used to estimate Core Damage Frequency (CDF) as the risk. The results of simulation is estimated quantitati vely as Cost of Electricity (COE), CDF, and consequence of Human Error in maintenance activities. And these results suggest it is useful to discuss how and when the components should be maintained.