NOVELTY - A pyrite cinder battery grade lithium iron phosphate manufacturing method involves adding steel discharging slag of sulfurous iron ore with reducing agent in low nitrogen atmosphere, or adding steel discharging slag of sulfurous iron ore with reducing gas comprising reducing gas of hydrogen/nitrogen or carbon monoxide/nitrogen. The resultant slag is subjected to acid leaching carried out by adding sulfuric acid to obtain acid leached product, which is filtered to obtain iron-containing solution, followed by removing impurity. The pH of the solution is adjusted by adding ammonia water.    USE - Method for manufacturing pyrite cinder battery grade lithium iron phosphate for use as lithium ion battery anode material.    ADVANTAGE - The method enables manufacturing pyrite cinder battery grade lithium iron phosphate with improved yield and better reliability in simple, safe and cost effective manner.    DETAILED DESCRIPTION - A pyrite cinder battery grade lithium iron phosphate manufacturing method involves adding steel discharging slag of sulfurous iron ore with 1-20 wt.% reducing agent in low nitrogen atmosphere, or adding steel discharging slag of sulfurous iron ore with reducing gas comprising 1-10% reducing gas of hydrogen/nitrogen or carbon monoxide/nitrogen. The resultant slag is subjected to acid leaching carried out at 60-80 degrees C by adding 20-80 mass% sulfuric acid for 10-200 minutes to obtain acid leached product. The acid leached product is filtered to obtain iron-containing solution, followed by removing impurity. The resultant solution is reacted at 5-90 degrees C for 30-120 minutes. The pH of the solution is adjusted to 1-4 by adding ammonia water. The 1-20 mass% leaching liquid is mixed with anionic polyacrylamide precipitate to obtain upper clear solution of ferrous sulfate solution. The ferrous sulfate solution is added with iron source, phosphorus source and lithium source at a ratio of 2-3:1:1 into a reaction kettle for hydrothermal synthesis reaction at 160-250 degrees C for 3-15 hours to obtain finished product, where the reducing agent is inorganic carbon source or organic carbon source.