Inorganic elements have a crucial impact on the yield and quality of crops by changing the secondary metabolic pathways during crop growth. The environmental characteristics of Guizhou Province are complex, and the inorganic elements of the understory soil in different regions are very different. Therefore, a fast and effective method is highly required to identify the differences in the inorganic elements of understory soil in those regions to provide theories for the selection of understory crops and planting requirements. This study used X-ray fluorescence spectroscopy (XRF) to detect inorganic elements in 12 samples of understory soils from 7 different regions in Guizhou Province. Totally 11 inorganic elements, including SiO2, Al2O3, Fe2O3, CaO, MgO, Ti, K2O, Co, P, Zn, and Cl, which are closely related to plant growth and development, were used to evaluate the adaptability of soil for planting crops. The results showed 23 elements in the understory soil in different areas of Guizhou, among which the major elements such as Si, Al and Fe comprised approximately 70% of the soil, and even more than 90% in some areas. Cluster analysis showed a certain correlation between the amount of soil inorganic elements and the region, and those regions can be clustered into 4 categories when the Euclidean distance was 6. Principal component analysis suggested that the higher soil scores in Dafang County of Bijie City and Liping County of Qiandongnan Prefecture are beneficial for understory crop growth and thus could be the key areas for the development of understory planting industries. This study suggested that X-ray fluorescence spectrometry can easily and effectively identify the composition of various inorganic elements in soil, explore the differences in element characteristics of understory soil, and provide references for under-forest crop planting in Guizhou Province.