Abstract: In order to determine the main influencing factors of the CO concentration change at the return air corner in Chahasu Coal Mine, taking 31209 fully mechanized mining face and 31313 fully mechanized mining face of Chahasu Coal Mine as examples, the influence degree of each mining technical condition on the CO concentration at the return air corner was quantitatively analyzed by the analysis method of grey system correlation degree from the mining technical condition. The results show that the main factor affecting the CO concentration at the return air corner is the air volume of the working face, and the correlation degree is 0.86 and 0.87 respectively. The other major factor is the surface atmospheric pressure, and its correlation degree is 0.82 and 0.86 respectively. The influence of daily advance rate and recovery rate is small, and the influence of air leakage rate on CO concentration in return air corner is not obvious.