Through analysis on the process of unsteady leakage of gas pipeline,the calculating model of unsteady leakage rate has been established.According to the variable characteristic of unsteady leakage ratio,based on the differential equation of on-flow diffusion,and combining the relevant original and boundary conditions,the diffusion model of unsteady leakage of gas pipeline has been established.Based on the practical application,all of the dangerous areas have been discussed and analyzed.The damaging and destroying areas have been calculated under definite conditions.This will provide safety standards and references for confirming and formulating the safety distance for the important buildings(school etc.) apart from the long high-pressure gas pipeline and main gas pipeline in city.At the same time,this will provide guarantee for reducing the dangerous degree,when accidents happened.