Abstract: According to coal been immersed in water, the phenomenon of coal spontaneous combustion would be highly increased in numbers. Based on No. 2-1 seam in Hulusu Mine as the study object,a coal spontaneous combustion simulation system was applied to test and measure CO and C2H4 productions of different moisture cont ent coal samples during the oxidized spontaneous combustion process and based on the CO concentration,the critical temperature of the coal spontaneous combustion wa s solved. The results showed that the moisture affected to the critical temperature of the coal spontaneous combustion would be double. With the moisture content of the C oal increased,the critical temperature of the coal spontaneous combustion would be firstly increased,then be reduced and then be increased. The optimum moisture conten t would be a minimum sometime. When the moisture content was higher than or lower than the optimum moisture content,the moisture content all could restrain the coal sp ontaneous combustion. The higher moisture content,the restraining function would be more obvious. The optimum moisture content of No. 2-1 coal spontaneous combustio n in Hulusu Mine was 12. 01%. When a water discharging and drainage conducted in goaf,the water content in the coal should be kept higher than the optimum moisture co ntent of the coal spontaneous combustion.