Abstract: Expansive soil is widely distributed in Yunnan Province, and a scientific analysis and characterization of its expansion and contraction characteristics are important for optimizing engineering design and construction. Through technical means of mathematical statistics such as statistical analysis, correlation analysis, and principal component analysis, the engineering properties and expansive potential of expansive soils in a high fill project in Yunnan are studied. A comprehensive formula for identifying expansive potential is established, and the expansive and contraction characteristics of these soils in the project area are illustrated. The results reveal that the expansive soil in this area features high water content, high void ratio, high plasticity, stiff-hard state, medium compressibility, and highly discrete expansion and contraction behaviors. The specific gravity of soil particles primarily influences the contraction deformation of soil, while a high proportion of clay minerals serves as the decisive factor governing the contraction deformation of expansive soils in the area. The established comprehensive identification formula developed in this study effectively captures the complex expansion and contraction characteristics of the expansive soils within the area, offering valuable reference for expansive soil identification and ensuring the safety and cost-effectiveness of engineering projects.