With a self-designed physical simulation test system for coal and gas outburst and instantaneous gas desorption of coal, orthogonal tests were designed and conducted to investigate the influences of initial gas pressure, coal particle size and outburst mouth

diameter on coal and gas outburst firstly, then gas pressure variation tests were conducted under different initial gas pressures and coal quantities to investigate the variation characteristics of gas pressure. The results show that the influence of outburst mouth diameter on the intensity and duration time of coal and gas outburst was biggest followed by coal particle size and initial gas pressure. The total outburst time was shorter when outburst mouth diameter was bigger, meanwhile the outburst intensity and outburst distance were larger when initial gas pressure was higher, coal particle size was smaller or outburst mouth diameter was larger. In some gas pressure variation tests, the maximum instantaneous gas pressure exceeded the initial gas pressure when the latter was larger, which means the initial gas pressure play a crucial role in coal and gas outburst initiation. Finally, the critical initial gas pressure and gas content were calculated as a reference to predict coal and gas outburst danger.