Abstract: Reliability centered maintenance（RCM） methodology has been applied to a service water system in AP1000 nuclear power plant.Using the functional failure modes and effect analysis（FMEA） and logic tree analysis（LTA）,the optimized maintenance strategy is established based on a better understanding of the relevant information on this system and related equipments（including the functional failures,failure modes and effects）conclude.Compared with the current maintenance strategy,this maintenance strategy optimized by RCM conducts the condition monitoring and periodical maintenance for dominant failures but conducts periodical test for the recessive failures.