The shear transfer pathway in the shear span of high-strength concrete beam was analyzed under shear failure to investigate the shear mechanical property of the inclined section of high-strength concrete beam. The contribution of high-strength concrete to the shear capacity of beam was considered based on the beam action and arch action. The stirrup contribution was determined by using the simplified modified compression field theory, and the influence of size effect was taken into consideration. Through the combination of concrete and stirrup terms, the calculation model for the shear capacity of high-strength concrete beam under concentrated load was established, which has a clear and reasonable physical significance. The effects of concrete strength, shear-span ratio, relative depth of shear compression zone, ratio of longitudinal reinforcement, ratio of stirrup, and size effect were comprehensively analyzed. In addition, the test data of 207 high-strength concrete beams with web reinforcement were employed to evaluate the proposed calculation model, and compared with the prediction results of GB 50010—2010, ACI 318-19, EN 1992-1-1:2004, Zararis formula, and Zsutty formula. Results show that the proposed model could reflect the shear failure mechanism of the inclined section of beam and predict the shear capacity of high-strength concrete beams. Besides, the model was less sensitive to the wide range variation of shear parameters, and the prediction accuracy had no obvious correlation. Thus, in combination with beam-arch action and simplified modified compression field theory, the proposed shear model can be used to calculate the shear capacity of high-strength concrete beams with high accuracy and stability.