Physical simulation experiment is important method to the second migration and accumulation of oil and gas. Physical simulation experiment of the natural gas is also an important field and its research is insufficient. Its research can indicate the exploration of the west of our country and have an influence on the policy of "the west gas to east". The paper studies the Nanbaxian and Mahai natural gas field and forms their accumulation model. It draw a conclusion that in the foreland basin of the west contrast with unconformity and permeable strata the fault is dominance channel; the Nanbaxian gas field has a character so called discrepance gathering. Many factors brings about it, including the anisotropy of the fault, the trap lacking of valuable height and having the fault connect to the surface.