Flow coefficient of nozzle is one of key parameters of water mist nozzle for design and type selection. It also determines water mist characteristics and accordingly influence the fire-extinguishing ability of water mist directly. In order to investigate the relationship between flow coefficient of nozzle and water mist characteristics, a series of experiments were performed by using multi-nozzle and single nozzle water mist with different flow coefficients(K=1.0, 2.5). The spray angle, flux distribution, particle size distribution were measured and compared. The experimental results showed that, with increasing of flow coefficient, the characteristics of multi-nozzle and single nozzle water mist were all changed.