An iron phosphate preparation method relates to the field of new energy material preparation, and comprises the following steps: mixing a ferrous sulfate solution and a phosphorus source in proportion, performing stirring to react for 10-120 min, adding an adjusting solution, adjusting the pH value to 3-7, performing filtering and washing to obtain ferrous phosphate; transferring ferrous phosphate into a reaction kettle, adding an impurity removing agent and a complexing agent, supplementing a phosphorus source according to a ratio of P to Fe of 1: 1-1.5: 1, then adding an oxidizing agent which is obtained by oxidizing ferrous iron into ferric iron with a stoichiometric ratio of 1.0-1.5 times, adding an adjusting solution, adjusting the pH value to 1.5-3.5, carrying out heat preservation for 30-90 minutes, heating to 80-100 DEG C, performing forming for 30-180 minutes, and carrying out precipitating, filtering, washing and drying to obtain finished ferric phosphate dihydrate; and carrying out heat preservation on the Ferric phosphate dihydrate at the temperature of 400 DEG C- and 750 DEG C for 30-360 minutes to obtain an anhydrous iron phosphate finished product. Heavy metal ions can be efficiently removed, so that the purity of iron phosphate is effectively ensured.