Small and modular reactor (SMR) has several features that are designed to improve the safety and security of the plant. However, the decrease in size and smaller facilities may cause undesirable consequences once a security incident happen. Therefore, the SMR security system should satisfy both the need of security integrity and cost-effectiveness. This paper suggests a new physical protection system strategy and evaluation to model SMR plant security cost and reliability of the system. An influence diagram has been developed to model the SMR characteristics and cost-effective allocation of security measures. Case study then developed to evaluate the plant’s reliability against security threats and compare security cost of different scenario. The proposed methodology has shown to be able to identify the most effective physical protection system to be established in a SMR facility. These methods and case study have implications in suggesting new security protection measures, improved SMR security system evaluation model, and a cost evaluation tool to evaluate the SMR security implementation strategy.