Abstract: The upheaval damage of subgrades of high-speed railways caused by muddy water on weakly expansive foundations has become another key factor hindering the development of China's high-speed railways. It is of great significance for the design and construction of high-speed railways to evaluate the swelling property of mudstone correctly. The equivalent montmorillonite content, cation exchange capacity, free expansion rate and liquid limit are selected as the indexes of swelling property of mudstone based on the Lanzhou-Urumqi High-Speed Railway. The grading standard for swelling expansion potential of mudstone is proposed based on a large number of field measured data of mudstone borehole. The combined weights of discriminant indexes are determined by the improved analytic hierarchy process, Gini coefficient method and relative entropy theory. A quantitative evaluation model for the swelling property of mudstone is established based on the linear comprehensive evaluation method. The results show that there is a certain linear relationship between the discriminative indexes, and it has good classification characteristics as a discriminant and classification index of mudstone. The classification standard for swelling potential of mudstone can realize the consistency of three indexes for samples of 94%. The linear comprehensive evaluation method overcomes the shortcomings of different indexes of the same sample belonging to different levels. It can quantify the swelling property of mudstone and obtains quantitative classification standard for swelling potential of mudstone. The applicability and accuracy of the quantitative evaluation and grading method for swelling property of mudstone of the Lanzhou-Urumqi High-Speed Rail way are verified by laboratory swelling force tests. The research results may provide a theoretical basis for engineering control measures of long-term continuous arch deformation in subgrades of high-speed railways with similar geological conditions.