An outburst of coal and gas in underground coal mines may occur when stress condition and coal failure combine with rapid gas desorption.A mechanical and fluid coupled numerical simulator, SimBurst, has been developed to simulate the initiation process of the outburst, as a first step to model the whole process of the outburst.This paper describes the simulator and a simple model set up to model the initiation of an outburst in roadway excavation to illustrate the methodology and approach with the SimBurst.The model simulated the basic features of an outburst initiation process, including coal deformation, pore pressure and principal stress vector redistribution, yield and tensile failure zone of coal, and a quantitative relationship among critical gas content, stress regime and coal strength.