Abstract: By defining the inclined section where shear failure occurs in concrete beam without web reinforcement, the flexural behavior of the section is analyzed. And failure pattern of the section is predicted based on the bending moments in cracking and ultimate states. Then the shear capacity of the concrete beam is determined corresponding to the failing moment of the section. To simplify the calculation, a formula is proposed for shear capacity of concrete beams under concentrated loads. The rationality of the proposed formula is analyzed using test data of 680 concrete beams, and the reliability index is further evaluated by probability method. Results indicate that the proposed method is applicable for predicting the shear capacity of concrete beams without web reinforcement. The calculation results are similar to those of the relevant standards in the United Stated and Europe, and are equally conservative. The calculated shear capacity can meet the reliability index requirements of structural components that fail in brittleness with safety level II. This research can provide theoretical basis and design formula for the stipulation of new version standards in China.