Abstract: Critical temperature is an important indicator to represent spontaneous combustion of coal.It is an accurate and efficient testing method,based on programming temperature,to calculate critical temperature through the changes of CO concentration and temperature.The paper analyzed coal particle size,moisture content and gas flow,which can get some influence to the critical temperature.finally.The best experimental conditions were determined,that was 0.12~0.18 mm of coal particle size,50 ℃ of dry temperature,100 mL/min of the flow rate.