The equilibrium hydrate formation conditions for ternary simulated flue gas [CO2 (0.1368) + N-2 (0.8547) SO2 (0.0085)] with SO2 aqueous solutions, and SO2 + tetra-n-butyl ammonium bromide (TBAB) aqueous solutions were measured using the temperature search method, over the temperature and pressure range of (272.85 to 283.15) K and (1.20 to 5.09) MPa, respectively. The corresponding equilibrium gas compositions were analyzed. The effects of SO2 concentration and TBAB additive on the hydrate phase equilibrium were studied. For the flue gas and SO2 aqueous solution, the presence of SO2 reduces the hydrate formation pressure. The higher is the SO2 concentration in aqueous solution, the easier the hydrate forms, and the higher the SO2 concentration in equilibrium gas phase is. N-2 mole fractions in equilibrium gas phase are higher than that in the feed flue gas, while CO2 is lower due to its relative high solubility. For a given system, the equilibrium hydrates formation pressure increases with the increase in temperature. Both SO2 and N-2 mole fractions in equilibrium gas phase decrease with the increase in pressure, while the CO2 mole fraction increases. TBAB solution with w(4) = 0.050 not only reduces the equilibrium hydrates formation pressure markedly, but also helps the dissolution of SO2 in aqueous solution. The SO2 concentrations in equilibrium gas phase for the TBAB addition system are much smaller than those without TBAB addition. The pressure reducing effect of the TBAB promoter for SO2 containing flue gas is dependent on the SO2 concentration and smaller than that for flue gas without SO2. A small amount of SO2 produces a synergy with TBAB to promote the hydrate formation, but the high SO2 concentration produces an inhibition on the hydrate formation, and causes the hydrate equilibrium pressure increase. The optimum SO2 mass fraction in solution is lower than 0.010.