For the marine power plant with the side exhaust system cooled by water spraying, the opening of the water spray cooling device will cause significant change of the temperature in the system. The properties of the flue gas in the exhaust system will therefore change, which accordingly affects the acoustic performance of the side exhaust silencer system. This paper firstly calculates the hydrodynamics of the side exhaust system before and after the water spraying through Fluent, and then the temperature distribution of the side exhaust silencer system at the different water spray flow by changing the cooling water flow. The CFD results are then used as the input to calculate the transmission loss of the exhaust system in order to obtain the acoustic performance of the side exhaust system before and after water spraying. It concludes that the water spry cooling can improve the acoustical behavior of the whole system at the low frequency range. The results can provide reference for the design of the side exhaust system in the future.