Abstract: In order to investigate the gas pressure effect on the process of coal and gas outburst, similar simulation experiments were carried out for coal and gas outburst under the conditions of 5 different gas pressure and 3 axial stress with self-developed simulation test system and large medium hard coal sample when the moisture content, proportioning, coal sample forming pressure and other parameters are constant. Experiments show that there is a gas pressure threshold, when the coal and gas outburst exceeds this threshold, the higher the gas pressure becomes, the greater the relative intensity of outburst happens, and relative intensity and gas pressure shows positive index, gas pressure has a certain degree of crushing and conveying of extruded pulverized coal as the outburst dynamic, can form obpyriform outburst hole with small mouth and large venter, and the axial stress has a positive role on the outburst of gas-bearing medium hard coal.