Metallocene-catalyzed poly-α-olefin (mPAO), one of the important base oils for its excellent lubrication performance, plays a critical role in modern industrial lubricants. Current research focuses on the impact of the molecular composition of the base oil, as well as its molecular structure on lubrication properties. However, the fundamental mechanism of the influence of mPAO structures at the molecular level, such as the polymerization degrees and the length of side chains on the lubrication performance, has not been fully studied. This work aims to investigate the lubrication mechanism of mPAO films with different configurations at the friction interface by employing the molecular dynamics simulation methods. The molecular viscosity increases by raising the polymerization degree (n=2, 3, 4, 5) with the same length of the side chain of mPAOs. Under shear friction (with smooth iron plates as friction pairs), by increasing the polymerization degree, the mPAO film at the frictional interface has much more complex molecular structures with a higher entanglement state. Meanwhile, the side chains of mPAOs show less opportunities to form a parallel and orderly distributed state, which will reduce the mobility of mPAOs during the friction process. As a result, the mPAO film presents better stability and higher internal frictional forces.On the other hand, when the polymerization degree of mPAO is the same, the longer the side chain, the higher the molecular viscosity. At the same time, due to the increased length of the side chain, the mPAO film also presents complex structures at the molecular level. Eventually, the complex network structure among mPAOs hinders the shear movement of the lubrication film during the frictional process, which furtherly enhances the stability and lubrication properties of the lubrication film. Therefore, with careful selection of molecular structures of mPAOs, particularly with proper polymerization degrees and branch lengths, the corresponding viscosity and lubrication performance can be optimized. This work provides a significant theoretical basis for understanding the structure-activity relationship of mPAO lubricants and also gives molecular insights for the design of industrial applications, which is critical for the development of efficient lubricant products.