With recent developments in sprinkler technology, water mist system is becoming more and more useful in fire suppressions. However, regulations on water mist system are inadequate, because most of them are based on experimental results. The computational method is an efficient way to make validations and optimize droplet size distribution of water mists. In this work, a computational fluid dynamics (CFD) model and a fire dynamics simulator (FDS) code were used to analyze effects of fire suppression using water mists with different droplet sizes. By using numerical methods, the interaction between water mist and fire could be better understood. The range of droplet size was determined based on the NFPA 750 standard. The fire extinguishing times of different droplet sizes were calculated by running the FDS code. After running the FDS code for different droplet size ranges, the optimal droplet size range was obtained. With the increase of droplet sizes, the fire extinguishing time first fluctuated and then increased. An optimal droplet size range was determined to have the best suppression effectiveness with the shortest fire extinguishing time and less water consumption. It should be noted that there are limitations for the CFD study since the real circumstance of fire is more complicated. (C) 2016 Elsevier Ltd. All rights reserved.