Abstract: In order to define the critical value of driling cuttings gas desorption indices which predicted gas outburst risk, based on the physical meaning explanatio n of drilling cuttings gas desorption indices and the desorption regulation of the No.2 coal seam in Tunlan Coal Mine, the relationship of the indices, the gas desorption quantity and the gas pressure were obtained.Through the theoretical calculation and actual mining situation, the outburst of the No.2 coal seam was characterised by hi gh gas pressure and low gas content.The critical value of gas pressure which could indicate the outburst was given.The critical value of drilling cuttings gas desorption i ndices were calculated, 0.18 mL/ (g-min0.5)for K1 and 95 Pa for Oh2.The field application showed that the identified critical value was more accurate for the outburst P erdiction, which could better guarantee the safety mining.