Liner cavitation is caused by water pressure fluctuation in the water coolant passage of the internal combustion engine. When the negative pressure falls below the saturated vapour pressure, the impulsive pressure following the implosion of cavitation bubbles causes cavitation erosion of the wet cylinder liner surface. The present work establishes a numerical model for structural-acoustic coupling between the engine block and the acoustic field in the water coolant passage considering their dynamic characteristics. The coupling effect is evaluated through mutual interaction terms that are calculated from the mode shapes of the acoustic pressure and engine block vibration on the boundary. Water pressure fluctuation of the fully assembled engine containing rotating shaft system is estimated considering all excitation forces and the contribution of the piston slap force to the water pressure response is discussed. It is revealed that the pressure fluctuation and liner vibration are mainly induced by piston slap forces in the operating condition. Moreover the influence of sound speed variations on the water pressure response are discussed.