A mathmatical model of the flow field of gas explosion is established. Applying themodified TVD (total variation diminishing) scheme of finite difference, simulation is conducted ofthe attenuation law of peak waves along underground workings, a law which best describes re-turn shocks and hence the acyual process of explosion . From the result, gas explosion and es-pecially return shock in mine can be understood clearly. The shock is formed at the source ofgas explosion with the value of peak shock decreasing with time and then return shock pro-duces at the negative pressure area. With the strength of return shock larger than normal pres-sure, the pressure of air in the undergound workings tends to become stabilized after the returnshock. The pressure of peak shock and return shock also decrease with increase of distanceand finally it approachs to normal pressure of the air. The attenuation rate of peak shock fol-lowr the law that it decreases along the workings. Because the destruction of mine vehicles dueto return shock is on the base of first shock, the design of mine ventilation system should takenotice of that and make some measures to prevent further loss.