Abstract: Phase characteristics of ship radiated-noise demodulation spectrum harmonic components are considered. By analyzing a large number of ship radiated noise data,it is found that the sum phase of line spectrum at shaft frequency and its some harmonic subtracts the phase of blade frequency line spectrum is zero or other constant in the demodulation spectrum,which is called phase coupling.Higher-order cumulant of the harmonic signal with phase coupling relationship is given,and higher-order spectrum of the harmonic signal is simulated.The application of phase coupling relationship is studied.According to the higher-order spectral analysis of some weak modulated ship radiated noise,it is indicated that using the phase coupling relationship can improve the ability to extract propeller parameter,especially for weak modulated ship radiated noise.