Herein, the highly dispersed ball-on-flake nanostructured ZIF-7/g-C3N4 nanocomposites were successfully constructed by two-step approach, i.e. the electrostatic adsorption (the first step) and in-situ preparation(the second step). The composition and structure of ZIF-7/g-C3N4 nanocomposites were determined by a series of characterizations (such as XRD, FT-IR, TGA, Zeta potential, XPS, SEM, TEM, etc). The dispersibility and interface compatibility of ZIF-7/g-C3N4 nanocomposites in base oil (150SN) were intensively probed by Uv-vis spectra and optical microscope, demonstrating that the ZIF-7/g-C3N4 nanocomposites had a superior interface compatibility in oil. Furthermore, the tribological properties of ZIF-7/g-C3N4 nanocomposites as additives in base oil were detailedly evaluated on a four-ball friction tester. The experimental results showed that the ZIF-7/g-C3N4 nanocomposites at 0.05 wt% optimum adding content exerted the reduction by 46.85% of average friction coefficient and 48.74% of wear scar diameter, while exhibiting the improvement by 18.37% of bearing capacity in base oil. In terms of the characterizations of the worn surface (such as FESEM, 3D profile, elemental mapping, XPS, etc), the lubrication mechanism of ZIF-7/g-C3N4 nanocomposites were deeply discussed and proposed, are attributed to its good dispersibility in base oil, assuming the existence of synergistic lubrication.