Abstract: Polysulfide olefins were synthesized and purified using 60~140 ℃ distillation range of FCC gasoline and industrial grade sulfur as raw materials in the presence of various basic catalysts. The possible synthesis and purification reaction processes were discussed. The synthetic reaction conditions were optimized and the thermal decomposition behavior of polysulfide olefins was studied. The results show that the sulfur content of polysulfide olefins is 30.03% with a density of 0.953 g/cm using sodium hydroxide catalyst under the reaction conditions of 170 ℃, the reaction time of 3 h, the sulfur and FCC distillate gasoline mass ratio of 0.45:1 and the basic catalyst and distillate mass ratio of 0.15:1. The Polysulfide olefins has a good oil solubility and a wide range of decomposition temperature (190-260 ℃) and can be applied to the presulfurization of hydrogenation catalyst.