With the rapid oil and gas industry development, the city gas pipeline has become a necessary infrastructure of the modern city. The Pipe leakage emergency rescue often involving multiple people and departments at all levels, also a large number of geographical space data for piping around. The Geographic Information System (GIS) has many advantages that it can conduct spatial data management, data visualization, analysis, simulation, and integrating with other systems. The main study line is simulating the gas diffusion, firing and exposing, once leaking, researching to the establishment of accident prevention, reducing damage caused by an accident emergency rescue system of city natural gas pipeline. The system can make a visual show of the assessment area of accident consequence with different grades through inputting physical and chemical parameters of natural gas, initial state of gas leakage and weather conditions.