Abstract: In this paper, we used the technique of the polynomial chirplet transform (PCT) to extract the instantaneous characteristics of the output response of the nonlinear system. Combined with estimation methods of instantaneous parameters in the PREEVIB and FROCEVIB methods, we acquired the back-bone curve and damping curve which reflects nonlinearities of the system. Then based on fitting of the identified average nonlinear characteristic forces, the specific parameters can be obtained. Numerical simulations results validate the effectiveness of this method, and it has advantages on high accuracy and good tolerance to noise.