Abstract:Molecular weight and polymer dispersion of Olefin Copolymers(OCP)and Styrene butadiene Copolymers(SDC) type viscosity index improver were measured by Gel Chromatography. The kinematic viscosity and apparent viscosity of OCP and SDC in four groups of base oils were measured by the method of determination of kinematic viscosity and apparent viscosity at high temperature and high shear rate. A European diesel injector apparatus was used to measure the shear stability at 100 ℃,and the cold cranking simulator were used to measure the low temperature dynamic viscosity of -15 ℃and -20 ℃.The results indicate that SDC has smaller molecular weight and larger dispersion than OCP, and the viscosity-temperature characteristics and shear stability of SDC are better than that of OCP in the same base oils. In four groups of base oils, the viscosity-temperature characteristics of OCP and SDC are showed GroupⅣ > GroupⅢ > GroupⅠ,the thickened characteristics are indicated Group Ⅳ> Group Ⅰ>Group Ⅲ>Group Ⅱ,the shear stability is stated Group Ⅳ >Group Ⅲ>Group Ⅱ>Group Ⅰ.The dynamic viscosity of OCP and SDC thickened oil at low temperature of -15 ℃ and 20 ℃ is equal to the corresponding base oils.