The leaking rate is crucial for the determination of emergency zone and leakage control measures，but most of the existing calculation methods were based on the conditions of steady leaking or dynamic leaking after a simultaneous closure of emergency shut down(ESD) valves.Hence，an equivalent model of gas leakage combined with process of natural gas pipeline is established by using HYSYS simulative software，and the leaking rates in steady and dynamic states are calculated under conditions of closure delays for ESD valves. Results showed that the closure delay of ESD valves has obvious effects on the leaking rates and the flow rates in pipeline，and countercurrent flows would occur in pipeline with the increase in the release hole size.The closure delay of ESD valves has little effect on release duration.