Abstract: Effects of ultrafine water mist on the explosion process were studied by visualization experiments. Two kinds of atomization methods were used to produce the ultrafine water mist and the mist size was measured by PDPA to real-ize the explosion analysis under certain water mist parameter conditions. It was found that the ultrafine water mist re-sulted in two opposite effects on methane explosion. The explosion intensity was indirectly affected through the influ-ence of ultrafine water mist on flame front structure. The effect degree of ultrafine water mist on the flame front was re-lated to water mist parameters (i. e. droplet diameter,velocity and spraying concentration). The flame was divided into four kinds of structures after the addition of water mist. In order to effectively realize the explosion suppression,it should make it be a small scale turbulent flame,so it is an advantage to achieve a good heat exchange and not cause obvious changes in the flame structure. The pressure rise is corresponding to the flame propagation. Meanwhile,the effects of mist parameter on the explosion overpressure,the two peak valves of pressure rising rate history and flame propagation velocity were significant.