Accurate calculation of shear strength of reinforced concrete (RC) circular columns plays a key role in the ductile seismic design, which can effectively prevent the occurrence of brittle shear and flexure-shear failure. Based on the existing quasi-static test results of RC circular columns, the seismic failure modes and the method for determining the shear strength capacity of RC circular columns are analyzed. On the basis of theoretical analysis, a shear strength model of RC circular column considering the effects of inelastic deformation (displacement ductility) is proposed and compared with the existing model. The results show that the shear strength capacity of RC circular columns decreases with the increase of deformation in the plastic hinge region under seismic loading. The shear strength capacity of flexural-shear failure columns depends on the lateral load corresponding to the shear failure point of the plastic hinge region rather than peak lateral load of the skeleton curve. The proposed model is able to effectively reflect the effects of deformation on the shear strength capacity of RC circular columns. And the results are in good agreement with the experimental data and can be used to predict the shear strength capacity of RC circular columns with different failure modes under seismic excitations.