This article demonstrates the influence of the molar ratio between diether as internal donor and Magnesium dichloride in processing of the catalyst preparation on the catalytic performance for propylene polymerization with MgCl2-supported Ziegler-Natta catalyst. The effect of electron donor on catalyst is investigated. The experimental data find that diether content on catalyst increases and Ti content on catalyst decreases with the increase of diether/Mg molar ratio. This result indicates that diether as internal donor is not coordinated to Ti species but to Mg species on catalyst. The introduction of diether remarkably improves the catalytic activity. The extents of improvement closely connect with diether/Mg molar ratio. The stereospecificity of catalyst intensively depends on the structure of diether as internal donor. The possible model of multi-active sites on heterogeneous Ziegler-Natta catalyst is proposed to explain these phenomena. (c) 2005 Wiley Periodicals, Inc.