The landscape boundary is a transition zone between two or more adjacent ecosystems, or an interface that exists between an organism and abiotic environment; it is also extremely sensitive to climate change and human interference, and plays an essential role in the structure, processes, and functions of ecosystems. Soil temperature affects vegetation growth, and plays an important role in environmental microclimates and plant production, and affects various chemical reactions of soil organic matter and nitrogen accumulation; therefore, it affects plant growth, seed germination, and crop output. Cultivated grassland-cropland boundaries (Maiping County, Guiyang) in Karst areas of Guizhou Province were analyzed, and the surface soil temperature (0-20 cm) of the interface was monitored seasonally. Moving-split window technology (MSWT) was used to compute the variables in adjacent samples along transect data, which was a simple and reliable method for determining the boundary, and MSWT could be used for any type of variable reaction. The width of the cultivated grassland-cropland boundary was determined based on soil temperature by combining the field measurement, indoor statistics, and MSWT in this study. The soil temperature of three functional areas in the study area was compared and analyzed. The results showed that the average annual soil temperature of the cultivated grassland-cropland boundary in Guizhou was 9.8, 26.5, 15.4, and 4.8℃ for spring, summer, autumn, and winter, respectively. The width variation of the soil temperature boundary in cultivated grassland-cropland varied with seasonal shifts and soil temperature, from wide to narrow: 37, 32, 27, and 24 m in spring, summer, autumn, and winter, respectively. This also indicated that the soil temperature-interface width in cultivated grassland systems varied consistently with the total width of the cultivated grassland-cropland boundary, which was categorized as a gradual changing boundary type. The average soil temperature of the cropland functional area, cultivated grassland-cropland compound functional area, and the grassland functional area was 14.0, 14.1, and 13.9℃, respectively, and the soil temperature of the three functional areas was significantly different in spring, summer, and winter; and the soil temperature in the grassland functional area system and cultivated grassland-cropland compound functional area were not significantly different in autumn, and the soil temperature in the farmland functional area system and cultivated grassland-cropland compound functional area were significantly different to the grassland functional area system. Based on these results, regarding the policy of "returning cropland to grassland", an optimal width of 12-18 m could be set for grassland-cropland intercropping in the studied area, and this study provides reference values for the sustainable development of southern grassland animal husbandry, and theoretical references and practical measures for enriching the boundary theory and the project of "returning cropland to grassland".