Abstract: According to the need that the drained coal mine methane should be mixed, diluted and added into the thermal counterflow oxidation unit to oxidize, it designed the drained coal mine methane diluting mixer with velocity difference by using the idea of vortex forced mixing. Through the method of numerical simulation, it studied methane distribution in pipe after the mixer. For the actual situation of operating parameters fluctuations in coal mine site, it discussed the operating parameters, such as methane velocity ratio between inner and outer pipe, inlet methane density and so on, then it studied the effect that drained coal mine methane and air flow adjusting system to the mixing efficiency. Results showed that the concentration of methane decreased from the axis to the wall in pipes, the uniformity of methane distribution increased along the way; the smaller the ratio of inner velocity to outer velocity was, the more uniform the concentration field was; the non-uniform index increased with the increasing of inlet methane concentration; while, the non-uniform index decreased with the increasing of inlet methane concentration when it utilized the flow automatically adjusting system of inlet air and inlet methane. So it ensured the drained coal mine methane diluting mixer with velocity difference to promote methane distribution uniform effectively with the drained coal mine methane and air flow automatically adjusting system.