Abstract: Experiments were carried out on YZ4DB3 diesel engine. The indicator diagram and emission of diesel engine fueled with ethanol/diesel blends were measured. The combustion process and emission of ethanol/diesel blends were analyzed. The results showed that with the increase of ethanol ratios, the ignition delay periods were delayed, the combustion endings were advanced and the combustion durations were shortened. At low load, the peak in-cylinder pressure of E10 and E20 were 0.2 and 0.4 MPa lower than that of diesel, the peak heat release rate of diffusion combustion increased. At full load, the peak in-cylinder pressure of ethanol/diesel blends were almost the same as that of diesel, the peak heat release rate of premixed combustion increased. Compared with diesel, smoke of ethanol/diesel blends reduced significantly. Ethanol ratios had little effect on NOx emission. With the increase of ethanol ratios HC and CO emission increased, especially at low load. The fuel consumption of ethanol/diesel blends and diesel were almost the same.