The invention relates to a method for preparing a lithium iron phosphate material, which is characterized in that: a dispersant in an amount which is 0.01 to 20 percent based on the mass of the precursor used for preparing the lithium iron phosphate is added into the precursor; and after, mixing, dispersing, drying and heat treatment, the high-performance lithium iron phosphate nano material is obtained; the dispersant is one or more of polyaminoamidophosphate, product of addition of fatty acid and epoxyethane, polyethylene glycol polyol, phosphate, polycarboxylic acids, organic phosphorus single-preparation antiincrustation corrosion inhibitors, organic phosphate, polycarboxylic acid antiscale dispersants, water treatment dispersant and dye dispersant; and the precursor may be a lithium-containing precursor, an iron-containing precursor or phosphor-containing precursor. When the method is adopted, the solid content of the precursor of the lithium iron phosphate material can be improved to over 35 percent, the high flowability of the precursor of the lithium iron phosphate material is maintained, and after the heat treatment, the impurity content is controllable. The lithium iron phosphate nano material has a spherical micro-nano structure, high tap density and high material processing performance.