Abstract: The Bunsen reaction liquid-liquid phase separation is an important part for the iodine-sulfur cycle, and the separation effect of sulfuric acid and hydroiodic acid directly affects the thermal efficiency of the whole cyclic system. To improve the separation effect and thermal efficiency, the characteristics of liquid-liquid phase separation when the Bunsen reaction is equilibrium were investigated. The mixture solution including sulfuric acid, hydroiodic acid, iodine and water was prepared, and the influence of different-experimental conditions on the liquid-liquid phase separation effect was investigated. The experimental results show that the excess iodine content for the liquid-liquid phase separation changes little when the mole ratio of water to sulfuric acid is less than 18, and then the excess iodine increases obviously with temperature and excess water in the feed. Reducing the excess water, at the same time increasing the temperature and the excess iodine in the feed can effectively improve separation effect of the solution. Increasing the excess water can also inhibit the side reaction, as the temperature increasing, inhibitory effect is more and more obvious. Through the experimental study, ideal separation conditions were got.