Abstract: In order to study the influence of different clay mineral contents in low clay mineral content mudstone foundation on the swelling potential and swelling upper arch deformation of ballastless track subgrade of high-speed railway, supplement and improve the existing standards for the determination and classification of ballastless expansive soil. Mudstone samples were selected from 25 typical roadbed arch diseased sections to conduct X-ray diffraction experiments. The free expansion rate experiment and cation exchange capacity experiment were optimized. The principal component analysis (PCA) method was used to extract the cumulative variance interpretation amount of 90.098% for dimension reduction analysis. And combined with the actual project to classify the interval. The results show that: PCA can exclude the influence of co-linearity between factors on the model results. Based on statistical significance, three factors can be used to characterize the good linear relationship between the swelling potential of expansive soil and micro-factors; by simplifying and optimizing physical indicators, the obtained index F for expansive soil has a Person correlation with the amount of arch on the actual track increased to 0.902; according to the actual expansion conditions of the line and the expansion grade interval divided by F, the accuracy of the judgment of the existing standards is significantly improved. The research results can provide reference and theoretical support for the identification of the expansive soil and disaster prevention along the high-speed railway.