When using minimum quantity lubrication (MQL) to assist ceramic tools in high-speed cutting of difficult-to-machine materials, the limited cooling and lubrication efficiency of base lubricant make it difficult to effectively alleviate ceramic tool stress concentration and ensure machining surface quality. In this work, Cu nanosheets were prepared through hydrothermal method and characterized. Boron nitride (BN) particles with flake, granular, spherical morphologies, and Cu nanosheets were dispersed in the LB2000 biodegradable base oil to prepare Cu/BN composite nano-fluids. The wettability and tribological properties testing of the developed nano-fluids confirmed that contact angle of lubricant decreased by 35.44% at most, with the addition of Cu/flake-BN hybrid nanoparticles compared to that of LB2000. Notably, the Cu/spherical-BN composite nano-fluids demonstrated superior anti-wear properties. Owing to the excellent lubricating performance of Cu/flake-BN composite nano-fluids, the surface roughness, cutting temperature and tool wear were significantly reduced. In addition, compared to the application of Cu/flake BN composite nano-fluids with MQL, Cu/spherical BN composite nano-fluids further decreased the cutting force by 22.41%. Analysis of tool wear mechanisms revealed that Cu/BN(flake) composite nano-fluids can significantly reduce adhesive wear and breakage region compared to composite nano-fluids containing spherical BN or granular BN, owing to the higher continuity and stability of the soft-hard flake composite lubricating film structure formed by soft-phase Cu nanosheets and hard-phase BN at the cutting interface.