Abstract: In view of accident characteristics of urban gas pipeline networks, principle and basic assumption to set up risk evaluation system as well as primary steps are dissertated.Conception of relative risk coefficient and its counting method in W.Kent Muhlbauer Scoring Method are introduced, also including parameters' significance in failure aggregate score, leakage impact coefficient, medium dangeous coefficient and diffusion coefficient and their reciprocal relationships as well.In the light the the inconformity items in W.Kent Muhlbauer KENT Scoring Method used to assess the actuality of urban gas pipeline networks in W.Kent Muhlbauer China, based on the influence of history leakage record, loss behavior of sabotage, environment risk, operating pressure and personal error on the establishment of risk evaluation indexse system, method to amend the indexse system in W.Kent Muhlbauer Scoring Method is put forward, which can be taken as a reference for risk evaluation of urban gas pipeline networks.