Abstract: Based on the analysis of the experimental results and on the equilibrium equations,this paper presents a theoretical model for the shear strength of reinfored concrete and reinforced fiber concerete beams.This model takes into account such factors as the height and stress distribution of shear compression region,the horizontal length of diagonal crack,the action of aggregate interlock and d owel forces.This model gives a clear concept,and is easy to understand as well as in agreement with experimental results.