Abstract: Molecular dynamics simulation is an important approach to study the viscosity characteristics of nanofluids but its computation scale is huge. In this paper, the computation scale is significantly reduced by applying the Martini force field on water-based fluid and coarse-graining water molecules. The micromotion of copper nanoclusters in water-based fluid was simulated based on the equilibrium molecular dynamics. The viscosities of Cu-H₂O nanofluids were calculated through the Green-Kubo formula. The effects of fluid temperature, volume fraction, shape and size of the particles on the viscosities of Cu-H₂O nanofluids were studied, based on which the existing empirical formula of the viscosity of suspension was modified.