Abstract: Long-term operation characteristics of the filtered containment venting system (FCVS) is important for mitigating the severe accident. To research the long-term thermal-hydraulic characteristics of FCVS with periodically open-and-close-venting strategy, a typical FCVS under assumed severe accident was simulated by using the thermal-hydraulic code RELAP5. Further, the effects of initial fluid level, environment temperature and decay heat power on the operation characteristics were researched by sensitivity analysis. The results show that the FCVS can achieve stably the periodic operation up to 250 hours under the assumed accident. By sensitivity analysis, it is found that in order to ensure the normal operation of FCVS, the initial fluid level should be changed with different environment temperature, and the decay heat power should be controlled within a certain range. This research may provide guides for the operation and optimization of FCVS and the safety analysis of nuclear power plants.