Abstract: Frame-tube structures are widely adopted in tall buildings since they can utilize the whole width of the structures to resist the overturning moment caused by lateral loading. A large amount of calculation is needed, if the structures are treated as three-dimensional space-frame structures in nonlinear analysis. Taking the structures as a whole to be analyzed will reduce the amount of calculation, but the problem will become complicated because of the occurrence of shear lag which is caused by the flexural and shear flexibilities of the frame members. In this paper, the shear lag coefficients are calculated through equivalent membranes analogy. Based on Timoshenko beam theory and multi-vertical-line-element model, a simplified nonlinear element model is proposed. In this model, shear lags in web and flange are considered. The amount of calculation is greatly reduced and the model is suitable for quick evaluation of frame-tube structures in nonlinear analysis during the preliminary design stage.