A titanocene complex of η5-pentamethylcyclopentadienyltri—P—chlorophynoxy—titanium[Cp*Ti(O-C6H4-Cl-p)3] was used in combination with methylaluminoxane (MAO) as cocatalyst to catalyze propylene polymerization．The effects of polymerization conditions such as temperature and Al／Ti molar ratio(nAL／nTi)on catalytic activity and molecular weight of polypropylene obtained were investigated．It was found that under the given polymerization conditions the molecular weight of polypropylene increased as the polymerization proceeded at the early stage

and the molecular weight distribution remained narrow(Mw／Mn=1．5～1．8)

which displayed the behavior of quasi—living polymerization；while the bimodal GPC profiles indicated a multi—site system at the early stage．In addition

a kinetics equation was presented to study propylene polymerizations at the depressing stage of polymerization rate

and the depressing coefficients under various conditions were obtained．With the depressing coefficient

the polymerization rate could be estimated at any time of the depressing stage．