In this paper, poly-alpha-olefins oil base stocks with medium kinematic viscosity and high viscosity index were prepared by 1-decene oligomerization catalyzed using the alkylaluminum chloride catalyst promoted by haloalkane and metal chlorides (VCl3, CrCl3, and TiCl3). The promotion effects of haloalkane and metal chlorides on oligomerization activity and properties of the oligomers formed were investigated. The small amount of VCl3 added into the EtAlCl2 -CHCl3 catalyst can increase the oligomerization yield from 85.90 to 94.18% and viscosity index from 152 to 158, accompanied by a slight decrease in viscosity. VCl3 enhances the activation of EtAlCl2-CHCl3 through the formation of bimetallic species containing two Al-Cl-V bridging bonds, which can increase release ability of carbocations from CHCl3 to promote activity and improve viscosity-temperature performance of the oligomers formed. The oligomer structure characterized by H-1 and C-13 NMR spectra indicates that the oligomerization of 1-decene on the EtAlCl2-CHCl3-VCl3 catalyst follows the cationic polymerization mechanism. The main oligomers formed are internal olefins with trisubstituted vinylene, which are formed as a result of chain propagation and rearrangement followed by termination. The metal chloride promoter just adjusts the distribution of the unsaturated bonds formed through different reaction pathways without change of the polymerization mechanism.