Abstract: Highly compacted bentonite is a type of clay aggregate material, and the micromechanical properties of its aggregates are critical to the buffering performance of soils in high-level waste repositories. The nanoindentation technique provides a new means to investigate the micromechanical properties of compacted bentonite aggregates. In this paper, the process of a Berkovich indenter pressing into the surface of a bentonite aggregate was simulated using the COMSOL finite element simulation software. Based on nanoindentation test data for 1.7 g·cm^-3 compacted bentonite aggregate, the microscopic modulus, Poisson's ratio, and yield strength were inversely calculated. The numerical model also simulated the effect of friction on nanoindentation test results. The results showed that the compacted bentonite aggregate exhibited distinct elastoplastic material behavior. The microscopic elastic moduli of Na-bentonite and Ca-bentonite aggregates obtained from numerical simulations were 2.0 GPa and 2.3 GPa, respectively, and the simulation results were approximately the same as the analytical solutions. The Poisson's ratio of the compacted bentonite aggregate was about 0.35, and the microscopic yield strengths of the Na-bentonite and Ca-bentonite aggregates were 167 MPa and 218 MPa, respectively. Tangential friction during nanoindentation testing had little effect on the measured micro-modulus. Numerical simulations provide the micromechanical properties of compacted bentonite aggregates and assist in the design and performance evaluation of the engineering barrier system for China's deep geological disposal of high-level radioactive waste.