The invention discloses preparation of self-support ultrathin two-dimensional efflorescent manganese oxide nanosheets and application of the self-support ultrathin two-dimensional efflorescent manganese oxide nanosheets in efficient wastewater purification. A 2D Delta-MnO2 nano-material is prepared from potassium ferrocyanide, potassium permanganate and diluted hydrochloric acid. The nano-materialcan effectively produce hydroxyl radicals, superoxide radicals and singlet oxygen radicals, releasing of lattice oxygen with high oxidation activity is accompanied, and then, the nano-material can rapidly degrade phenol, bisphenol A, methyl orange, acid blue, Coomassie brilliant blue, rhodamine b, ciprofloxacin, norfloxacin, enrofloxacin, ascorbic acid and the like in a wide pH value range of 2 to 11, wherein the degradation of the bisphenol A can reach a second level. An efflorescent self-support structure is formed by two-dimensional nanosheets through self assembly, and thus, a new way isopened up for fine adjustment on structures and properties of two-dimensional materials; and the preparation method is simple in operation, short in cycle and high in economic benefit, thereby being applicable to large-scale production.