The invention relates to a method for determining iron content in a silicon nitride material, wherein microwave digestion is adopted to carry out a sample pretreatment, and an inductively coupled plasma mass spectrometer is adopted to determine iron impurity content in silicon nitride. The method specifically comprises: weighing a silicon nitride sample, adding HNO3 and HF, adopting microwave digestion to treat the silicon nitride sample to obtain a sample solution, adding a Sc internal standard solution, diluting to obtain a solution requiring detection, adopting a random sample to carry out a blank test, adopting single crystal silicon to carry out backing, adding the equivalent Sc internal standard solution to each standard solution to prepare a series of standard solutions of iron, selecting working conditions of an inductively coupled plasma mass spectrometer, analyzing the series of the standard solutions according to the concentration range from the low concentration to the high concentration to obtain an iron working curve, analyzing the blank solution and the silicon nitride solution requiring detection, substituting into the working curve to calculate to obtain the Fe concentration value in the blank solution and the Fe concentration value in the solution requiring detection, and calculating to obtain the mass percentage of the iron in the sample requiring detection. The method has characteristics of high accuracy and good reproducibility.