Recently some experiments of extinguishing class K fires with water mist are carried out [1,6-8]. It is necessary to thoroughly investigate the interaction of water mist with class K fires, and disclose the related principles so as to provide scientific guidance for the use of water mist in kitchens. The purpose of this work was to develop a water mist system to effectively extinguish cooking oil fires. In order to achieve this purpose, the mechanisms of water mist in extinguishing cooking oil fires were investigated, and the impact of pool fire characteristics on the effectiveness of water mist in suppressing cooking oil.