Abstract: In order to analyze the reasons of delay outburst of coal and gas, a combination model composed of “barrier layer and soft coal” is established. The model demonstrates that it is the barrier layer between the work space and the soft coal that defers the occurrence of an outburst accident. The damage of the barrier layer needs a period of time to cause the exposure of the soft coal and finally lead to a delay outburst. According to the combination model, the effect of barrier layer thickness on delay time is analyzed using the method of numerical simulation. Result shows that the barrier layer enters into the acceleration creep in a shorter time as the thickness of the barrier layer decreases. Therefore, in order to prevent a delay outburst, the miners should support the roof very fast after a relatively long driving footage which results in a thin barrier layer.