The invention relates to a perfluorinated acid substance determination method. The perfluorinated acid substance determination method includes the steps of (1), preparing a solution to be determined; (2), preparing a standard solution; (3), sucking the standard solution precisely, determining the standard solution according to liquid chromatography-mass spectrography, and drawing a standard curve according to determination results; sucking the solution to be determined precisely, determining the solution to be determined according to liquid chromatography-mass spectrography, and computing the content of perfluorinated acid substances in the solution to be determined according to detection results and the standard curve. The perfluorinated acid substance determination method has the advantages that the method is low in detection limit, good in reproducibility and high in adding standard recovery ratio, the detection limit reaches 0.01 mg/L, relative standard deviation of repeatability is less than 6%, and sample adding standard recovery ratio ranges from 90.7% to 108.5%.