In order to enhancement accuracy of shear design of reinforced concrete (RC) beams, detail understanding of the shear resistance mechanism is required. This study evaluated the shear resistance mechanism of RC beams based on arch and beam actions by using three dimensional Rigid-Body-Spring-Method (3-D RBSM). Firstly, RC deep and slender beams with and without shear reinforcement failed in shear were tested to measure local behavior. Then, the validity of local behaviors obtained from 3-D RBSM was confirmed by comparing with the test results and the applicability of decoupling of shear resistance mechanism using simulated stress distribution was presented. Moreover, the contributions of arch and beam actions in RC beams until failure stage were investigated numerically by changing the shear reinforcement ratio and shear span to depth ratio and was compared with the current shear design recommendations in JSCE Standard Specification. As a significant finding, the numerical results upon the quantitatively evaluation of shear resistance mechanisms that the shear strength of RC beam could be evaluated without classification of deep beams and slender beams was presented.