Abstract: The compositions of high viscosity PAO150 were determined by high temperature gas chromatography. The types and polymerization degree of PAO were analyzed by ASTM D7169. The atmospheric pressure boiling points of poly α-olefins with the degree of polymerization of 2-13 in the sample were calculated using CET (Chromatography Equivalent Temperature) method. The results indicate that there is a 1-decene polymer with polymerization degree of 2-16 in the sample and the boiling point of 1-decene polymer is 100 ℃ lower than that of paraffin with same carbon number when the polymerization degree is over 13. The high boiling point components in PAO150 are easy to cracking during the kettle-type distillation process, resulting in reduction of viscosity, viscosity index and relative molecular weight, but bromine index.