Abstract: In order to study the evolution mechanism of urban gas networks leakage disasters, a Bayesian network model of leakage disasters evolution was built. Types of disasters and damage targets were analyzed by counting the disasters, and the evolution chain of gas networks leakage disasters was established. Disaster factors during the evolution and their influence were identified,and the key nodes of the chain were analyzed though the evolution network structure. The results show that the gas networks leakage disasters are explosion, fire, suffocation, etc. And the main damage targets are residents' lives, buildings, other city lifelines, etc.The disaster evolution is the result of the effects of disaster environment factors, disaster - causing factors and disaster - affected factors. Leakage, fire disaster, explosion disaster, power supply facilities damage are the key nodes of the evolution chain of the urban gas networks leakage disasters.

Key words: urban gas networks, leakage disasters, evolution chain;evolution mechanism, key nodes