Abstract: In order to separate structural noise of ship hull structural nonlinear system, when considering its nonlinearity and response spectrum feature, this system is idealized into pure nonlinearity-input system. Volterra series is employed in its Generalized Frequency Response Functions (GFRFs), and nonlinear frequency spectrum features are obtained. Consequently the strategy of noise source analysis of nonlinear system is proposed. Finally and numerical simulation and experimental investigation are carried out, and the results show that, nonlinear frequency spectrum features are of reasonable existence, and the proposed strategy is reasonable and effective, which is able to simultaneously realize parameter estimations of the excitation source and GFRFs of the system. Both nonlinear frequency spectrum features and the proposed strategy of noise source analysis of nonlinear system lay the foundation of further discussing nonlinear feature extraction and its characteristic spectrum separation of ship hull structural noise.