Large amount of methane is emitted into the atmosphere by mine ventilation and methane drainage systems each year. In this paper, a mixer is developed, which can mix drained coal mine methane with ventilation air methane to be oxidized together in the thermal flow-reversal reactor. The mixing process and the effects of the structural parameters of the mixer on the mixing effect are numerical investigated. The calculation results indicate that reducing the maximum injector diameter will lead to worse uniformity of the mixture. While the uniformity can be improved with increasing the injector angle from 30 to 45 degree, and the improvement is more obvious by reducing the injecting hole diameter under the sum area of the injecting holes fixed. This work is helpful to improve the design of the mixer.