Aiming at the complex mechanism and operation characteristics of the mechanical system of diesel engine on RO-RO passenger ship， a multi-component nonlinear vibration signal decomposition method and vibration characteristic parameter extrac tion strategy are proposed. The signal is decomposed into intrinsic mode function （IMF） components via empirical mode decompo sition and restrained the end effects in empirical mode decomposition （EMD） by symmetrical extension. The sensitive component is extracted by the correlation. The characteristic frequencies are matched according to the amplitude demodulation spectrum via 4 order high energy operator （4th-HEO）. The proposed method is illustrated by the three-dimensional vibration signals under 0 load and 100 load operation conditions of the RO-RO passenger ship. The results show that the analysis performance of vertical signals are better than other axial signals. And for the 9-cylinder 4-stroke diesel engine， the amplitudes of 0.5 times and 4.5 times are very prominent， and are more sensitive to load changes.