Water mist technology provides efficient firefighting performance while there is still room for improvement, so varieties of additives have been studied recent years both abroad and domestic. The self-made additives are used to compare the firefighting performance of diesel and heptane fire in open space. By adjusting the concentration of substance in the additives and conducting the experiment under the pressure of 0.3 MPa, 0.5 MPa and 0.7 MPa, extinguishing time, flame shape and temperature are measured in the experiment. Through the experiments using different fuels, it can be found when the fuel is heptane who has a lower ignition point and a higher evaporation, the water mist additives can still significantly improve the firefighting performance. According to the data based on different concentrations of fluorinated surfactants, we can see fluorinated surfactants are the main substance to prove the performances by changing physical property of water mist. Maximize fire performance proportion of the additives are find by experiments results.