Abstract: Instead of conventional ductility, deformability is proposed for various load-deformation curves of members made of new materials, such as fiber reinforced polymer (FRP). After analyzing the existent performance indices, the design-aimed state and the ultimate failure state are defined as the characteristic behavior states for members. Moreover, a set of performance indices, including deformability factor D, strength factor S , deformation energy factor Y and overall performance factor F, are presented to describe the behavior and the safety storage of flexural members comprehensively. Comparing with the traditional members, the relation among the performance indices is analyzed by the numerical results of five types of members and the ranges of the indices are acquired. It is drawn that the safety storage for strength and deformation can be exchanged without overall safety margin loss. F factor is suggested to serve as the scale for determining the design-aimed state, by which the reasonable uniform safety storage for various flexural members can be acquired. It is proven by evaluating eight specimens in references. The proposal of the performance indices including deformability provides a reference for the design of members made of new materials.