Soil erosion on the Loess Plateau poses a significant environmental challenge, resulting in the surface presenting a form of thousands of gullies. The slope-gully system is a typical erosive landform in this region. Along the gully shoulder line (SL), the slope-gully system can be divided into the inter-gully area (IG) and gully area (G). Its transition zone characteristics lead to differences in soil properties and vegetation characteristics between the topographies, thereby influencing the root-soil complex shear resistance. However, the spatial heterogeneity of root-soil complex shear resistance across different topographic units in slope-gully systems, as well as its primary controlling factors, remain insufficiently understood. Therefore, this study selected the IG, SL, and G in sandy loam soil (Shenmu, SM), silty loam soil (Ansai, AS) and silty clay loam soil (Yongshou, YS) zones of the Loess Plateau to investigate the spatial heterogeneity of shear resistance and its dominant drivers. The results indicated that the shear capacity of the slope-gully system was jointly regulated by topographic, soil textural, and chemical factors. The shear resistance generally showed an increasing and then decreasing trend along IG, SL, and G, and the influence of topographic gradient on cohesion (c) showed different trends in different textured soils. Among them, SL exhibited significantly higher c than G in sandy loam soil (p < 0.05), while significant differences were observed between IG and G in silty loam soil (p < 0.05). Internal friction angle (phi) did not show significant topographic differences among different textured soils. Partial least squares path modeling further revealed that soil chemical properties (standardized path coefficient = 0.55) directly dominated the spatial differentiation of c, whereas phi was primarily controlled by soil textural parameters (standardized path coefficient = 0.36). These findings could provide a scientific basis for optimizing regional erosion management strategies and hold great significance for enhancing soil and water conservation efficiency.