In this paper, a consistent analytical model for tapered steel members with symmetric or asymmetric variations is proposed for the second-order inelastic analysis of steel structures. In past decades, the tapered steel members are modeled by stepped elements, which is time-consuming of model building and analysis. Simply modeling methods of tapered members were proposed to deal with symmetric and asymmetric variations respectively by previous studies. To unify the modeling method for symmetric and asymmetric variation, a consistent analytical model is proposed in this study. The model utilizes the flexibility-based beam-column element with initial member imperfection, which can get an accurate simulation for tapered members with symmetric or asymmetric variations in the elastic or elastic-plastic analysis. Besides, the model is appropriate for various patterns of initial member imperfection that varies from prismatic members, which will be convenient for the future research related to the influence on member resistance due to different initial imperfection patterns. Several examples are given in this paper to illustrate the accuracy and practicability.