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Pure molybdenum material was processed by high-pressure torsion（HPT）at room temperature under the applied pressure of 6 GPa with different revolution number of 1, 2 and 5 turns, and the ultrafine-grained molybdenum was obtained. Nanoidentation technology was applied to characterize the mechanical properties of HPT-processed samples as well as the sintered one. The load-displacement curves, hardness and elastic modulus were obtained directly. The stress-strain curves of different samples were obtained base on the finite element simulation by using the software of Abaqus. The results show that the hardness of HPT-processed samples has an obvious increase from 3.02 GPa to 7.80 GPa. Correspondingly, the yield strength increase significantly from 970 MPa to 3370 MPa. Grain refinement and dislocation tangling make the major contribution to the strength improvement. However, there is a gradual decrease in elastic modulus along with the increasing HPT revolutions, which may be due to the dislocation tangling and residual stress. The relationship between stress and equivalent strain during HPT was established based on the stress-strain curves obtained by simulation results, and the hardening behavior during HPT processing was discussed.