Commercially available lubricants mostly use low-polarity polyalphaolefin (PAO) and synthetic esters to enhance the tribological properties of the lubricating oil and the solubility of the additives to comprehensively improve the product performance. In order to simulate the tribological properties of synthetic oil in practical application and the action mechanism of synthetic ester, the nitride composite coating with high hardness, good wear resistance, good oxidation resistance, and anti-adhesion was selected. To explore the tribological properties and synergistic lubrication mechanism of CrN/TiN multilayer films under the action of synthetic oils with different viscosity. Polyalphaolefin was selected and compounded with trimethylolpropane esters (TME) to obtain synthetic oils of different viscosity gradients. The kinematic viscosity (40 ℃ and 100 ℃), pour point, flash point and surface functional groups of the synthetic oils were characterized with a fully automatic viscometer, a pour point tester, an open flash point tester and a Fourier transform infrared spectrometer (FTIR), respectively. The CrN/TiN multilayer films were prepared by the reactive magnetron sputtering technique, and the microstructures of the films were analyzed by means of X-ray diffraction diffractometer and FIB-TEM characterization, and the mechanical properties of the films were tested by nanoindentation. The tribological properties of the films under dry friction and oil lubrication conditions were characterized with a ball-on-disk tribometer. The characterization of element valence by XPS analysis of the wear scar. The synthetic oil obtained by the combination of PAO and TME had high viscosity index, low pour point and high flash point, indicating that it could be applied to a wide temperature range. The CrN/TiN film had a typical face-centered cubic (FCC) structure with a heterogeneous structure and a hardness of 32.2 GPa. The successful preparation of the film was demonstrated by characterizing the microscopic internal structure of the CrN/TiN film. The study of the solid-liquid composite lubrication system found that compared with the steel ball friction pair, the average friction coefficient decreased from 0.95 to 0.71 and the wear depth decreased from 25.0 μm to 16.8 μm after plating the CrN/TiN film on the surface under dry friction conditions. The addition of synthetic oil significantly reduced the friction coefficient of the two friction pairs, and the wear rate decreased gradually with the increase of the viscosity of synthetic oil. Because the ester group in the synthetic oil had strong polarity, it could be better adsorbed on the surface of the friction pair during the friction process to form a dense oil film. In addition, the high viscosity synthetic oil film led to the decrease of friction coefficient, which was consistent with the stribeck curve. For a series of high viscosity index synthetic oils with different viscosity obtained by compounding TME with high-performance PAO base oil, the wear rate and wear depth of CrN/TiN multilayer films decrease with the increase of the synthetic oil viscosity, and the anti-friction and anti-wear properties are significantly improved. XPS analysis of the wear tracks indicate that the adsorption of polar ester groups in the synthetic ester at the sliding interface enhances the load-bearing properties of the oil film and thus slows down the couple friction wear.