The invention provides a method for preparing a metal vanadate nano material. The method comprises the following steps: adding a surfactant into a vanadate XVO4 solution, slowly adding a metallic nitrate M(NO3)3 solution, and continuously stirring; after addition is completed, continuously stirring for reaction; leaving to stand and age, performing centrifugal separation, washing, and performing drying treatment, thereby obtaining the metal vanadate nano material, wherein a mixed solution of triethanolamine, glycerol and ethanol is adopted as the solvent of the vanadate XVO4 solution; M comprises one of Sm, La, Eu, Y, Tb, Gd and Bi; X comprises Na or K. The method provided by the invention is simple in preparation process, low in cost, narrow in particle size distribution of the obtained product, and good in industrial application prospect.