Abstract: The present invention provides a method for preparing battery-grade anhydrous iron phosphate from liquid crude monoammonium phosphate, and belongs to the technical field of chemical industry production. In the present invention, ferrous sulfate solution and liquid crude monoammonium phosphate are used as raw materials, and ferrous iron is oxidized to ferric iron and separates out iron phosphate precipitate under the action of an oxidizing agent to obtain iron phosphate intermediate slurry; and then battery-grade anhydrous iron phosphate is finally obtained through solid-liquid separation, washing, aging, solid-liquid separation, washing, drying, dehydration and breaking up. The method provided by the present invention realizes the resource utilization of liquid crude monoammonium phosphate, has simple process and convenient operation and produces less waste water.