In order to reduce the casualties and damage caused by gas leakage，and to get the diffu-lion law of gas leakage，a system model is constructed and tested based on similarity theory. Multiple regression analysis of the diffusion law of gas leak with temperature，humidity and other factors coupled based on the concentration of different spatial points and the gas leakage rate of gas pipeline have been done. The gas leakage diffusion equation has been established and been verified through the test repeatedly on similarity theory and dimensional analysis. This result of research has a reliable theoretical basis to probable gas leakage prediction and emergency relief measures.