A diesel engine chemical additive is composed of the following raw materials in parts by weight: 40 to 50 parts of ethanol, 20 to 30 parts of cyclohexanone, 5 to 10 parts of silicone oil, 10 to 15 parts of n-butanol, 1 to 5 parts of benzyl alcohol, 10 to 15 parts of S80, and 1 to 5 parts of petroleum sulfonate. The addition amount of the chemical additive is 0.1% of diesel oil, the chemical additive is suitable for passenger trucks, cargo trucks, trains, ships and tractor which take the diesel oil as the fuel, the oil saving rate of the chemical additive in trains and locomotives is 2% to 3%, and the oil saving rate of the chemical additive in automobiles and ships can reach 8% to 20%. The diesel engine chemical additive has the advantages of available raw material, low price, simple equipment and technology, good product stability, and easy promotion; has a prominent effect on strengthening the power, improves the cetane value, triggers the complete combustion, improves the thermal efficiency, and reduces the oil consumption. The oil consumption is more effectively saved for long-distance high-speed driving, and people can directly sense the oil-saving effect. Moreover, the discharging of CO, hydrocarbon compounds, NOx, and solid particles in the tail gas is greatly reduced, the environmental pollution is reduced, and thus the chemical addictive has a prominent economic benefit and social benefit.