Abstract: The methodology study of risk-informed in service inspection (RI-ISI) was presented in the paper. In the RI-ISI process, the risk insights were incorporated, and the risk matrix was employed to characterize the safety significance in two-dimension (i.e. rupture likelihood and consequences of assumed pipe ruptures). The inspection effectiveness and pertinence could be improved. The RI-ISI method was applied to pipes in primary circuit pressure boundary of unit 1 and 2 for Tianwan Power Plant. The evaluation results show that RI-ISI allows the plant to target its resources to inspection locations which are truly significant risk, and the in-service inspection workload and cost decrease. In addition, the irradiation doses to workers with in-service inspection programs can be keeping as low as reasonably achievable. Some suggestions on RI-ISI application were proposed in the end.