Abstract: According to the force theory of fog droplet in transverse airflow, the motion equation of a single droplet in the tunnel is built and solved by using Matlab, the motion trajectory of water mist with different sizes of droplets in the tunnel is also obtained. Based on the simulated test bench, the movement and diffusion experiment of water mist is conducted. Comparing the experimental value with the theoretical value of diffusion distance of water mist, the correctness of trajectory model of water mist in simulated roadway and solution is verified.