Abstract: Three dimensional numerical model of methane-air explosion was established by using the large eddy simu- lation model. The processes of water mist evaporation and vaporization and the exchanges of the mass,momentum and heat between the gas and liquid phases were considered. The continuous phase and discrete phase were calculated through the Euler-Lagrange model respectively and alternately solving two phases control equation to realize the gas- liquid two phases coupling solution. The effects of the mist size on the interaction extent and the heat exchange rate of explosion reaction zone were analyzed,and the optimum size for explosion suppression was obtained and the reason of the suppression effect difference was explained respectively. The effect of mist size on gas-liquid two phase heat ex- change rate was affected through the interaction extent of the flame reaction zone,the droplet and the evaporation rate; thereby the flame propagation speed and explosion intensity were affected obviously. The condition of mist size selec- tion was that the mist should be completely vaporized in the reaction zone in order to effectively realize explosion sup- pression.