The compressed wave produced by the flame in combustible vapour cloud opening to air was researched by numerical simulation. Based on the fact that the energy-releasing speed is limited in the process of deflagration produced by combustible vapour cloud opening to air

the mathematical models expressed by Euler equation was refined further via importing a “on-off” function

which means energy wave mode.The new mathematical model including “on-off” function not only reflects the deflagration characteristic of limited energy-releasing speed

but also simulates the whole deflagration process via a equation.The solution of the equation and a computational example were given.The computational results were more consistent with the results of model experiment than other model results. The simulation results showed that the deflagration of the combustible vapour cloud opening to air could only produce weak shock waves and was nonideal explosions different from ideal explosions.