Abstract: Aiming at the problems of unreasonable selection of gas desorption index critical value of drilling cuttings and its difficult confirmation in the field, the gas desorption indexes of drilling cuttings were tested under different gas adsorption pressure in the lab. The test results show that the gas desorption indexes of drilling cuttings present variation of power function type with the changes of gas pressure. Under the minimum outburst gas pressure, the lower the firmness coefficient of coal is, the higher the gas desorption index of drilling cuttings is. And, the gas desorption index critical region of drilling cuttings is 0.62, 0.76. With three rate method, the gas desorption index critical value of drilling cuttings of No.3 coal seam was tested and verified. The results indicate that it is reasonable that the gas desorption index critical value of drilling cuttings is 0.6 mL/(g·min^1/2).