Abstract: Calculations and experiments of free modes, constraint modes and wet modes were proceeded for a sandwich steel plate oil pan. Their well matching results show that, a coupled model is feasible. The comparison between coupled and uncoupled modes demonstrates that the modal shapes change and the entire modal frequencies decrease when taking the oil into account. The ordinary least square method was applied to fit the Rayleigh damping scale factors of the oil pan with and without oil, which indicated that the oil could hardly affect the damping of the sandwich steel plate oil pan. The vibration responses of coupled and uncoupled models calculated by multi-body dynamic method indicate that the entire acceleration amplitude is close to the experimental one as well as the variation trend. It is shown that the entire vibration of the coupled model is weaker, and is prominent below 500 Hz, especially in the vicinity of 330 Hz. Besides, the peak frequencies and the trend of the coupled model coincide with the experimental result much better. Furthermore, the comparison of the radiation noise calculated by the boundary element method demonstrates that an evident entire decline occurs after considering the oil in the range of 0~3 000 Hz except 333 Hz.