The invention belongs to the field of inorganic nonmetallic materials preparation, and relates to a preparing method of a yttrium manganese acid nanometer material. The method comprises the steps of fully dissolving yttrium acetylacetone and manganese acetylacetone in a methanol solution, conducting a solvothermal reaction, conducting filtering and washing, and then conducting drying and calcination cooling to obtain the yttrium manganese acid material. According to the preparing method of the yttrium manganese acid nanometer material, the technology is simple, convenient and easy, the product purity is high, the preparing cost is low, and the size of the yttrium managanese acid nanometer material is 20-30 nm; in addition, both the homogeneity and the dispersity of the product are good, the manufacturing technique is simple, the sintering temperature is low, and the yttrium manganese acid nanometer material can be easily applied to mass production in practice. As a photocatalytic material, the yttrium manganese acid nanometer material has a high catalytic activity and has wide application prospects in the field of degradation of dyestuff wastewater and indoor noxious gases, photocatalysis sterilization and the like.