Abstract: A dynamic blowdown model of natural gas venting system were developed using the process simulation software HYSYS Dynamic based on the natural gas pipeline of a real specified LNG terminal. The required orifice areas during the emergent blow down scenario were calculated and chosen. In addition, the dynamic response process of main variable parameters including pressure, temperature and actual relieving capacity with the time were discussed and researched. The analysis results showed that dynamic simulation could clearly reflect the main parameters of dynamic response during the blowdown process, predict the lowest temperature and maximum capacity of the medium accurately, and instruct the selection of the orifice areas and the pipeline material of natural gas blowdown system.