Abstract: The bearing capacity and mechanical behavior of inner-and-outer flanges subjected to tension and bending loads are studied. A semi-analytic computing method is derived based on plane-section assumption. The results achieved by this method are compared with those obtained using nonlinear finite element analysis (FEA). Mechanical characteristics of the inner-and-outer flange are revealed through investigation on the variation of rotation axis, neutral axis and bearing capacity with the axial tension force. Finally, the bearing capacities of a series of inner-and-outer flanges are computed and analyzed, and a calculation method is proposed for design of an inner-and-outer flange subjected to tension and bending loads. It is found that the flexural capacity of the inner-and-outer flange would decrease with an increasing tension force. Compared with FEA, the semi-analytic method has sufficient accuracy and higher computational efficiency. The proposed calculation method for design has higher reliability and accuracy, compared with the traditional method for computing the bearing capacity of rigid outer flanges. It can provide the basis for the design and calculation of inner-and-outer flanges.