Recent years，the safety of urban gas underground pipelines system becomes focous in many megapolises. However，the research on the assessment of urban underground pipeline systems is focoused on the serious accidents，such as leakage，fire or explosion for gas underground pipelines. There are few papers on the assessment of accidents of functional invalidation for urban gas underground pipeline systems. Using PSR model，the index system of hazard assessment was established by three aspects，namely the “pressure”，“status” and “response” of gas underground pipeline system. The assessment samples were classified firstly，then studied by the Support Vector Machine，and the classifying model was established. The samples that would be assessed were classified by the classifying model mentioned above. The class values of the samples classified were mapped to the hazard grade，which the assessment could be accomplished.