Abstract: In order to solve the problem of low oxygen in the first working face 5-20101 of Qinglongsi Coal Mine, in this paper, combined with the working face mining and the surrounding basic situation, it is found that the influence of atmospheric pressure change, low temperature oxidation of the residual coal in goaf, water and gas displacement in goaf and positive pressure fan ventilation in tail-lane are the important reasons for low oxygen in working face. Some technical measures have been taken, such as establishing the monitoring system of spontaneous combustion, reducing the negative pressure of mine ventilation, strengthening the sealing of air leakage above and below the mine, inerting the floating coal in the goaf, improving the progress of the working face and injecting nitrogen into the goaf, so as to effectively solve the problem of low oxygen in the mining process of the working face and ensure the safe production of the mine.