A new version of “Rules for the Prevention of Air Pollution Caused by Ships” published by International Maritime Organization (IMO) on January 1, 2015. The regulation stipulated that the allowable emissions of SOx from ships in the Global Emission Control Area (ECA) reduced from 1% to 0.1%, and the limitation on sulfur oxides in fuel oil used on board ships operating outside designated emission control areas will be reduced to 0.5%. Many technologies have been developed to meet the sulfur oxides limits by shipowners. Many types of devices are installed to reduce emission and to increase power efficiency, such as turbocharger, economizer, SCR, heat recovery system, catalytic converter, and scrubber etc. A turbocharger is a type of turbine-driven forced induction installation used to increase the power and efficiency of an internal combustion engine by intaking more air into the combustion chamber. SCR is a method for converting NOx into N2 and H2O in the presence of a catalyst. An exhaust heat recovery system is a technology that translates thermal losses in the exhaust pipeline into energy to save fuel and reduce CO2 emissions. Economizers are mechanical installations intended to reduce energy consumption or to preheat a fluid. A catalytic converter is a type of exhaust emission control device, and it is designed to convert toxic gases and pollutants into less toxic pollutants from the exhaust gas of an internal combustion engine by catalyzing a redox reaction. Installing a marine exhaust gas scrubber is the best measure with the lowest cost and higher efficiency to convert NOX into N2. Through a series of chemical and physical reactions, scrubber can clean up SOX and particulates produced by diesel engines. A lot of researches have been put into different types of scrubbers. As one of the best measure, scrubber technologies have been developed and commercialized. In this research, it was discussed that the influence of two different types of scrubber structures on pressure drop and flow streamlines. Pressure drop is a target related to the efficiency and power of diesel engine, and the flow streamlines is a target related to the duration for which the exhaust gas and cleaning water are in contact. It was also discussed the influence of the nozzle location and quantity on the cleaning water distribution. The length and number of horizontal and vertical baffles and the number and location of nozzles were calculated and analyzed. The optimal inner structure was found out after fluid analysis of the scrubber for small marine engine, which shows that an inner structure with a baffle length ratio of 0.6 with two baffles was considered optimal in the case of a horizontal scrubber, and a baffle length ratio of 0.7 with two baffles was considered optimal in the case of a vertical scrubber. The result shows that the horizontal location is better than the vertical location, and the case of the six nozzles has the best performance in analyzing the influence of the nozzle location and quantity.