Abstract: To study the effect of ethanol supply mode on exhaust emissions of high-speed diesel engine, an experimental study of the ethanol supply mode was investigated in a high-speed, small swirl chamber diesel. The contrast experiment was used to compare the discharge index among supplying ethanol alone, ethanol-blended fuel diesel, and diesel alone through inlet. Compared with the ethanol-blended fuel diesel, the soot emissions of supplying ethanol alone reduce 16% and CO emissions decrease 10%, while NOx and HC emissions increase. The soot emissions of ethanol supplying alone and ethanol-blended fuel diesel is much lower than supplying diesel alone. The supply mode of ethanol is an important element which affects the properties of high-speed diesel engines.The supply of ethanol through inlet can substantially reduce the emissions of soot and CO.