The invention provides a cleaning agent compound for a magnetic drum type magnetic filter and a preparation method of the compound. The cleaning agent compound comprises pure water, alkaline substances, EDTA (ethylene diamine tetraacetic acid) sodium salt, antioxidants, antirust agents, mineral oil, surface active agents and defoaming agents. The preparation method includes the steps: adding the antioxidants, the antirust agents and the surface active agents into the mineral oil at the temperature of 50-60 DEG C; uniformly stirring the antioxidants, the antirust agents, the surface active agents and the mineral oil, adding the pure water, the alkaline substances, the EDTA sodium salt and the defoaming agents, stirring the pure water, the alkaline substances, the EDTA sodium salt and the defoaming agents at the temperature of 60-70 DEG C, and sequentially filtering the mixture by a 300-mesh filter screen and a 5 micrometer filter bag to obtain the cleaning agent compound for the magnetic drum type magnetic filter. Compared with the prior art, the cleaning agent compound has the advantages that the pure water and the mineral oil serve as main components, the alkaline substances are added, the antioxidants, the EDTA sodium salt, the antirust agents, the surface active agents and the defoaming agents are used, the prepared cleaning agent has excellent cleaning property, good antirust property among normal working procedures and the like, and use requirements of the magnetic drum type magnetic filter for steel rolling are met.