The invention relates to a cleaning agent and a preparation method and application thereof, and belongs to the field of resource environment waste disposal. The cleaning agent is characterized by being prepared by adopting and sequentially mixing surface active agents such as sodium dodecyl sulfate and polyoxyethylene fatty alcohol sodium sulfate which have the effects of permeating, foaming and emulsifying, acid-alkali agents such as sodium hydroxide, potassium hydroxide and barium hydroxide which have the effect of regulating the acidity and alkalinity, moisturizing agents such as ethylene glycol and propylene glycol which have the effect of keeping the humidity and solvent such as isopropyl alcohol, ethyl alcohol and propylene glycol monomethyl ether which have the effect of dissolving. The cleaning agent and the preparation and application thereof have the advantages that the cleaning agent is sprayed to solid matter to be permeated and dissolved for 5-10 min and then smeared with a cleaning cloth, and advertising stickers, ink marks, pressure-sensitive adhesive marks, mark pen writing and the like on the surface of the solid matter can be quickly and conveniently removed.