There often exists initial deformation of various extents in a largedeformed structure with nonlinear components, which means the change of the system’s static equilibrium point. Moreover, under the initial deformation, in the dynamic differential equations will appear the cubic stiffness nonlinearity term and the asymmetric squared term. The experimental results show that a “softening” effect can be observed under the excitation of a quite small force. A numerical simulation was executed with the physical parameters in the experiment, which shows that the nonlinear frequency response changes from “hardening” to “softening” along with the increment of the initial deformation, and the critical deformation was computed; while “softening” to “hardening” with the increment of the amplitude of the exciting force. Under various initial deformations and amplitudes of the exciting force, superharmonic resonances and subharmonic resonances were observed.