Abstract：
In this paper，the simplified formulas of the flexural capacity are deduced by means of internal lever arm coefficient，based on the basic assumptions and equilibrium equations of reinforced concrete bending members.The influence of moment，the reinforcement ratio，the strength of the concrete is analyzed.Finally，the suggestions of suitable internal lever arm coefficient are put on condition that the reinforcement ratio of concrete beam is not greater than 1.6% in China，when calculating of reinforcement and the flexural capacities of concrete beams.Internal lever arm coefficient suggested is 0.80（C30 concrete，HRB 400 steel reinforcement）or 0.85（C35 concrete，HRB 400 steel reinforcement）.
