1-bromo-3,3,3-trifluoropropene with low extinguishing concentration has been identified, but it has high boiling points and is not suitable replacements for halon 1301. However, mixtures of 1-bromo-3,3,3-trifluoropropene in an inert gas could produce fire-extinguishing agents with many of the desirable properties of halon 1301. To study binary fire suppressants, one has to determine the extinguishing concentration of the 1-bromo-3,3,3-trifluoropropene/inert gas mixtures. In this study, a method based on cup-burner was used to estimate the extinguishing concentration of 1-bromo-3,3,3-trifluoropropene/inert gas mixtures. A mechanism for mixing 1-bromo-3,3,3-trifluoropropene with inert gas before applying to fire was proposed. The results show that addition of small amount of 1-bromo-3,3,3-trifluoropropene in inert gas reduces the extinguishing concentration of inert gas considerably, and 1-bromo-3,3,3-trifluoropropene/inert gas mixture suppressant shows strong synergistic interactions at low mole concentration of 1-bromo-3,3,3-trifluoropropene.