Abstract: Water mist for fire suppression and control has received considerable attention as one of the potential measures for replacing HALON. Information on volume mean diameter and coordinate component velocity of two types of water mist has been obtained by using LDA/APV system and the mechanism of fire suppression using water mist been explored with the aid of Cup Burner system. A series of experimental study has been conducted to observe the effectiveness of CH₄/air fire suppression using water mist. The results show that water mist consisting of 10～100 μm diameter droplets is an effective flame suppressant in a co-flow cup burner flame. The diameter and mass fraction of water mist significantly affect the temperature distribution of the methane CH₄/air flame. The effect of oxygen dilution is more prominent in the upper part of the flame, whereas, endothermic heat exchange with the droplets plays a critical role in the lower half of the diffusion flame.