Second-order effect of structural members is usually analyzed with a practical and effective elastic finite element method in the design of frame structure. The method considers the stiffness reduction of structural members, the structural geometric nonlinearity and the material nonlinearity, and its accuracy mainly depends on the rationality of stiffness reduction factor. Until now, there has no research on the stiffness reduction factor of the two-span bent structure. 34 typical single story equal-leg two-span bent columns were taken as the object to carry out the elastic second-order analysis and the nonlinear static analysis under the most unfavorable loads. Taking the equivalence of the entirety second-order effect as the target, a unified stiffness reduction ratio is suggested which is compliant to two-span bent columns. And the effectiveness of the elastic second-order method with considering stiffness reduction in two-span bent structure and the rationality of the stiffness reduction factor is proved through comparing the nonlinear analysis to multi two-span bent structures.