The invention relates to a preparation method of iron phosphate, which comprises the following steps: adopting iron sulfate and phosphoric acid as raw materials and oxydol as an oxide to be subject to complete oxidation, and adding sodium hydroxide to perform a reaction so as to obtain the iron phosphate. By adding excessive sodium hydroxide, iron in the solution can be subject to a basically complete reaction, thereby improving the utilization ratio of the raw material iron sulfate. The iron recovery rate of the product is up to 99.0%, and the product purity is up to 93%.