The invention provides a method to precisely control iron-loading capacity of iron protein succinylate. The iron-loading capacity of iron protein succinylate can be accurately and quantitatively determined through a calculation formula; the iron-loading capacity of iron protein succinylate may reach 15%; the method has good simplicity, good dissolubility and good quality stability. The method according to the application prevents complex measurements with large error, and the error is not higher than +/-1%.