In the field of equipment reliability management of the nuclear power plant, it is a very important concept to develop, optimize and implement the preventive maintenance program. As an important analysis method in the maintenance field, PMO (Preventive Maintenance Optimization) technology provides a technical method to quickly optimize preventive maintenance programs on the basis of the current PM (Preventive Maintenance) program. It improves the efficiency of preventive maintenance optimization and saves resources of investment under the premise of guaranteeing equipment reliability. This paper briefly introduces the seawater desalination system and then analyzes the application of PMO technology in detail, combined with the characteristics of the seawater desalination system. The preventive maintenance program of the seawater desalination system is comprehensively optimized. The usage reliability and water-making capability of the seawater desalination system’s components are effectively improved by PMO technology. It is significantly important for the safe and economic operation of nuclear power units and also provides an important tool to manage equipment reliability and optimize maintenance in the nuclear power field and other industrial fields.