Abstract: The laws of air-water mist heat transfer in the mine return air diffuser are studied by numerical simulation. According to the prototype of return air diffuser, a three-dimensional and simplified numerical model is established. On the basis of the confirmed diffuser's basic parameters, a reasonable boundary condition is set. The effect of water-air ratio on the heat transfer performance of air-water mist counter flow in the diffuser is simulated by Euler-Lagrange method，and the trends of airflow temperature field, velocity field, pressure field and droplet counter flow trajectory under different conditions in the diffuser is got. The results show that air-water mist heat exchange efficiency is better than the others in unchanged parameters when water-air ratio is 0.9. It is associated with the appropriate resistance, the best overall performance and the good agreement with actual project. Then the correct selection of the water-air ratio in engineering application is theoretically proved.