TiCl4 was reduced with ethylaluminum sesquichloride in n-hexane. The reduction product was treated with diisoamyl ether and by heating at 35℃ in TiCl4 solution. The comlex catalyst thus obtained gives high catalytic activity and stereospecificity for polymerization of propylene. The compositions and structure characters of the reaction product in the preparation process of catalyst were investigated. Moreover

the mechanism of the transformation of TiCl3 at the lower temperature was discussed.