Up to now

on Cossee's mechanism

the stable configuration of catalytical centre

the essence of propylene coordination

the process of chain propagation

effect of alkyl aluminim and even whether Cossee's mechanismis resonale or not have still not come to identical understanding. In present paper

a theoritical study of the mechanism of propylene polymerization with Ziegler-Natta catalyst has been investigated in terms of the ASED-MO method. Acoording to Cossee's model

the calculated results are basically in agreement with the experimental

so it can be considered to be rational. Moreover

there is need tofurther investigate the related key reactions to clarify the details of mechanism. It isshown that the stable configuration of ca-talytical centre is a trigonal bipyrimid andit is activated by coordinating ofpropylene mole-cule

to be r\transformedinto a octahedron. It is just a weak coordinated bond linked pro-pylene and Ti3+ in active species has not effect ofback-donated electrons. But coordinating propylene can change the charge distribution ofsystem to facilitate the polymer chain propaga-tion. The average activation energy of polymerization calculated is 59.2KJ.Mol-1.For some disputed proplems

explainations are also given.