The invention belongs to the field of petrochemical industry, and particularly relates to a primary oil aid, and primary oil and a preparation method thereof, wherein the primary oil aid comprises anantioxidant, a corrosion inhibitor, a detergent dispersant and a cosolvent, has good corrosion resistance, can be adsorbed on the inner surface of an engine so as to prevent the corrosive components in an oil product from corroding the engine, protect the engine and prolong the service life of the engine, and has good oxidation resistance. According to the invention, by combining the primary oil aid, isopentane, isohexane, isooctane, alkylated gasoline, methyl tert-butyl ether, raffinate oil and toluene to obtain primary oil, the primary oil aid can react with the unstable free radicals in theprimary oil to terminate the chain reaction in the fuel oxidation process and eliminate the free radicals, so that the primary oil is in a stable state, the storage time of the engine and the oil product is prolonged, and the good cold starting performance, the combustion performance and the power performance are achieved; and after the primary oil is combusted, the combustion efficiency of the engine is high, the oil consumption is low, and the tail gas emission is little.