Root ecological niche characteristics are an important basis for the selection of slope protection plants, and the combination of plants with different root types has ecological niche differences due to the root structure, which directly affects the plant's effect of soil retention and restoration on slopes. In this experiment, four commonly used slope protection plants with different root types as case study: Amorpha fruticosa L. with a vertical axis root type, Lespedeza bicolor Turcz. with a horizontal axis root type, Medicago sativa L. with a root tillers type, and Festuca arundinacea with a tufted root type. The planting method involved simulated wet spraying on slopes is used to study the ecological characteristics of different root system combinations. By clarifying the intricate relationship between different types of roots and their ecological functions, the study provides a reference for selecting plants for slope restoration and reinforcement of slope stability. The results show that: (1) There is a significant difference in the distribution of different root structure types in various soil layers. In the soil layer at a 0-10 cm depth, GG (Festuca arundinacea) exhibited a significantly higher percentage of root length and root dry weight than other combinations, at 86.9% and 90.83% respectively. Meanwhile, in the soil layer below 5 cm, ZM (Amorpha fruticosa L.+Medicago sativa L.) showed significantly higher than other combinations, at 63.73% and 76.52% respectively. (2) The root niche index decreased as the number of radial levels increased, displaying an inverse J-shaped. The root niche index of GG and HH (Lespedeza bicolor Turcz.) initially increased and then decreased with soil depth, whereas the other combinations decreased with increasing soil depth. GG showed the most substantial change in vertical spatial niche, with a range of 0.21-3.51. In soil layers less than 10 cm deep, except for ZM, the niche index of the other combinations significantly decreased, indicating a surface aggregation niche type. Similarly, all position index decreased significantly, suggesting a surface aggregation ecological position type. (3) The combination with the highest overall ecological niche index after normalization was ZH (Amorpha fruticosa L.+Lespedeza bicolor Turcz.), which was 1. Additionally, the only three plant combinations of ZHG (Amorpha fruticosa L.+Lespedeza bicolor Turcz.+Festuca arundinacea) had significantly higher fine-root niche index, niche width, and subsurface interspecific competition index than the other combinations, with values of 0.089, 0.036, and 0.438, respectively. When combining the niche characteristics of different plant combinations with various root types, the better-performing root type combinations out of the 9 combinations were: vertical-axis-root type+horizontal-axis-root type (ZH), vertical axis root type+horizontal axis root type+clumping type (ZHG), root tillers type (MM), and vertical axis root type+root tillers type (ZM).