Abstract: When modeling the slender structures such as cable and tether with large flexibility, the complex twirling geometry in practical situation is usually ignored and the cable is simplified as a general beam with homogeneous material. In doing so, the result of dynamic simulation diverges from the physical significance. Therefore, this paper provides an equivalent dynamic method for the typical nonlinear helix wire strand considering the inner line contact under the static and large scale dynamic conditions. The variable bending stiffness affected by the contact friction and bending curvature is obtained through the equivalent constitutive law, by which the massive computation resulting from fine modeling method is able to be avoided. Based on the absolute nodal coordinate formulation, a series of the generalized coordinates have been selected to establish the dynamic differential equations. To verify the equivalent method, a fine strand model based on the finite segment element has been provided to test the accuracy according to the practical strand configuration. Furtherer, the distribution of the variable bending stiffness in practical strand under certain load is obtained through the quasi-static analysis. Compared with traditional ANCF model, the dynamic simulation of the one-tip-fixed equivalent beam under gravity coincides with the fact that the stiffness decreases as well as the flexibility increases in twirling strand. At last, the conversion among each kind of the energy component has been researched. The equivalent model of the twirling strand with large deformation can be used to improve the efficiency of the motion prediction in cable dynamic systems. Besides, the results provide the evidence for wire rope design.