The numerical simulation method of analyzing the effect of barrier on diffusion due to pipeline failure and the model for diffusion of natural gas had been established using species transport and reaction module of Fluent. By practical reconnaissance, the predigested 2D geometric model for barrier was established. Furthermore, the effect of barrier on diffusion of natural gas was obtained by comparison of simulation results (such as the distribution of natural gas and velocities in the case of barrier or no barrier). The simulation results can provide reference for dealing with the leakage of natural gas due to pipeline failure.