A fire developing tendency mathematical model of mine fire zone under positive pressure ventilation was established and was validated based on the particularly serious fire accident of Fuhua “9.20” in Heilongjiang province. Then the law of positive pressure ventilation influence on the fire zone developing tendency and its enlightenment to work safety were obtained. Under positive pressure ventilation, high temperature fire source has an obvious tendency to spread toward the gob, but with the development of fire, the aerotactic movement of combustion makes the high temperature fire source zone also slowly spread toward the roadway of mine. As the fire developing, a lot of smoke flows into the roadway, and distension of high temperature gas accelerates the gas flow rate in the roadway. The acceleration directly results in the spread and diffusion velocity of gas in the ventilation system, which will aggravate the accident.