Abstract: The interaction mechanism of ultrafine water mist and methane / air explosion flame in a closed vessel was numerically modeled. Large eddy model and partially premixed combustion model were used to calculate the explosion flow field and the methane / air combustion. In order to describe the mass,the momentum and energy exchanges be- tween the gas and liquid phases,the Euler-Lagrange model was used to couple the continuous and discrete phase equa- tions. The calculation result was verified and the enhancing and suppressing mechanism of water mist on explosion was analyzed in detail. Results show that the latent heat absorption is the dominant mechanism followed by the sensible heat absorption by water vapor,and relative to the momentum absorption by water mist;the two opposite results of en- hancement and suppression on explosion can be attributed to the combined effect of heat absorption and vaporizing ex- pansion of mist;and the droplet size,velocity and mist concentration have an obvious effect on the temperature,thermal diffusivity,fluctuation velocity and turbulence scale of flame front,and further affect the flame speed as well as the thermal increasing rate of the vessel.