The invention relates to a reclaimed cleaning agent capable of reactivating a ternary catalytic converter, prolonging the service life of the ternary catalytic converter, increasing the automobile power and lowering the oil consumption. The reclaimed cleaning agent is prepared from the following components in percentage by weight: 60% of methanol, 25% of ethanol, 7% of toluene and 8% of cyclohexane. The methanol and ethanol have the main function of generating oxygen ions in the combustion process of an engine combustion chamber, the toluene and cyclohexane have the main function of generating free alkyl radicals in the combustion process of the engine combustion chamber, and the combination of the oxygen ions and free alkyl radicals can remove the substances covered on the surface of the ternary catalytic converter more effectively. The preparation method of the cleaning agent comprises the following steps: mixing the raw materials at normal temperature, and sufficiently stirring uniformly.