Abstract: To investigate reinforcement buckling and influential factors of reinforced concrete (RC) columns under seismic loading, a simplified calculation model of longitudinal bar buckling length considering the nonlinearity of reinforcing bar is proposed based on minimal energy principle. Seventy three rectangular RC columns with different reinforcement layouts are adopted to verify the reliability of simplified buckling model. The simplified calculation model is compared with the model proposed by Dhakal and Maekawa (D&M model). The results indicate that, the longitudinal bar will be in nonlinear period during buckling, and the equivalent elastic modulus of longitudinal bar is 0.025 times the initial elastic modulus of steel through error analysis. The lateral confinement of stirrups on longitudinal bars can be simplified as linear springs, stiffness of which is related with the cross section area and stirrups layouts. Simplified calculation model can predict the buckling length of longitudinal bars with good precision, which is better than D&M model.