Abstract: In order to analyze the atomization characteristics and dust suppression efficiency of air-water spray in un- derground coal mine,the atomization characteristics and dust suppression efficiency of air-water spray were theoretical- ly investigated in a systematical way based on fluid dynamics,multiphase flow and aerosolology. Based on the theories of fluid dynamics and multiphase flow,a complete equation set of nozzle flow rate was derived,and the formulas for calculating the size and velocity of droplet were provided. The theoretical calculating formula of classification efficiency was derived by establishing the mathematical model of air-water spray dust-setting,and the relationship curves between classification efficiency and influence factors were drawn using Origin software. At the same time,combined with the distribution formulas of particle size and frequency,the theoretical calculating formulas for calculating the dust sup- pression efficiencies of total dust and respirable dust were also established. At last,the influences of medium diameter and distribution index on dust suppression were analyzed.