Abstract: In order to clarify the shear resistance mechanism of a high-strength stirrup concrete beam, this study applied a three-dimensional rigid-body-spring-method (3D RBSM) to evaluate the shear strength, the failure mode, the critical diagonal crack pattern and the ultimate deformation capacity of the beams reinforced by normal-strength (HRB235) and high-strength (HRB500) stirrup. The study results indicate that the improvement of shear strength and deformation capacity due to high-strength stirrup usage is not significant (<6% and 13%) compared with normal-strength stirrup. Moreover, this study quantitatively evaluated the shear contributions of the beam and arch actions at each loading stage for each beam. It was found that the beam action is dominated by stirrup shear contributionV_s while the arch action dominates the grade of shear strength and is identified as the key-shear contribution. Compared with normal-strength stirrup, high-strength stirrup with extremely high yield strength of 900 MPa leads to 29.7% increase in V_s, but has no significant improvement on arch action (<11.0%) which depends on concrete compressive strength nearby loading point. Finally, it was proved that current shear design for concrete member adopts the lower limit of test database with an intention to ensure the safety, but it does not rationally evaluate beam and arch actions and ignores the relationship between the arch action and the concrete contribution/stirrup ratio, and therefore needs further improvement.