Abstract: Hazards and potential influence areas of high-pressure natural gas pipeline leaks depend on the mode of leak, gas release, diffusion conditions and ignition methods. Taking the urban gas pipeline in service as an example, impacts of natural gas pipeline leaks are analyzed based on two cases of combustion and diffusion. potential influence areas and those for jet fire and vapor cloud diffusion under the condition of 15 cm-hole leak and pipeline pressures of 3.5 MPa and 4.0 MPa are calculated and represented graphically. The results show that in the case of a 15 cm-hole leak, it is safe more than 200 m from the pipeline at all events. Warning regions could be defined and emergency plans formulated based on this.