The invention discloses a preparation method of a lithium iron phosphate anode material used in a lithium-ion power battery. The preparation method takes ammonium dihydrogen phosphate and lithium carbonate or lithium hydroxide or lithium acetate and ferrous oxalate or ferrous acetate or takes the lithium dihydrogen phosphate and the ferrous oxalate or ferrous acetate as raw materials, the raw materials are prepared according to the ratio of Li, P and Fe of 1:1:1 or the ratio of LiH2PO4 to Fe of 1:1, and is added with micro amount of nano-metallic oxide or metal salt. After the process of mixing by a water wet method, spraying, drying, rolling and prilling, the mixture is pre-sintered for 10 minus or plus 2 hours at the constant temperature of 300-400 DEG C and is clad with carbon for prilling after being cooled; and then after the process of mixing by the water wet method, spraying, drying, rolling and prilling, the mixture is sintered for 10 minus or plus 2 hours at the temperature of 650-800 DEG C and then is cooled to obtain the lithium iron phosphate which is made after being crashed by gas stream and being compacted. The preparation method has the prominent advantages of safe preparation process, simple operation procedure, easy realization of industrialization and stable material performance of the product.