This research includes an experimental study and a nonlinear analysis using the finite element method of reinforced concrete beams with large opening in body that exist in shear zone . The tested beams are simply supported with rectangular section and without additional reinforcement in opening region. The opening is square in shape with variable dimensions and constant distance from the support . Studying the effect of changing length of the opening on the behavior of the reinforced concrete beams was already completed. The modes of cracks , (load-deflection ) relationship, ultimate load and the mode of failure for all beams were determinate . The study showed that existence an opening in shear region of beams reduce the strength of beams and affect on the mode of shear failure , and any addition in the depth of the opening lead to early cracks , more deflections and less ultimate failure load .