When expansive agent was put into limited space, its volume can expand after hydration reaction. The pressures caused by the expansion can reach to more than 50 MPa to ambient medium, and its increasing process was in the nature of typical dynamic character. The reason caused coal and gas outburst was that elastic strain energy stored in coal seam originally releasing suddenly when the condition of stress was changed. The physical process of coal and gas outburst was simulated in the test through expansive agent dynamic loading. The results indicated that the test method of dynamic loading of expansive agent in limited space can simulate the coal stress and boundary conditions of outburst truly, which was a good test method to study the coal and gas outburst problems .