Abstract: Abstract：【Objective】To reveal the differences in hydrodynamic characteristics between eluvial horizons and parent material horizons of subalpine meadows caused by engineering excavation under different slope gradients, and to clarify their erosion dynamic mechanisms. 【Method】 Indoor simulated rainfall experiments (90 mm/h) were conducted to systematically determine runoff hydrodynamic parameters (Re, Fr, τ, f, ω) and erosion rate (Dr) on two types of slopes under 8°, 15°, and 25° gradients, and to analyze the influence of slope gradient on the erosion process. 【Results】(1) Response of hydrodynamic parameters: The Reynolds number (Re) of the parent material horizon was 25.2% and 16.6% lower than that of the eluvial horizon at 8° and 25° slopes, respectively; the Froude number (Fr) showed slope-dependent changes (decreasing by 41.9% at 8° and increasing by 22.7% at 25°); the shear stress (τ) increased by 12.4% at 8° slope but decreased by 35.6% at 25° slope. (2) Erosion dynamic characteristics: The resistance coefficient (f) of the parent material horizon increased significantly by 164.8% at 8° slope, leading to a 23.3% increase in Dr; however, at 25° slope, f decreased by 42.1%, resulting in a Dr increase (104%) that was significantly lower than that of the eluvial horizon (257%). (3) Erosion patterns: The Dr of the eluvial horizon showed a monotonically increasing trend with slope gradient (8.44–30.17 g.m⁻².min⁻¹), while the Dr of the parent material horizon became lower than that of the eluvial horizon when the slope was ≥15°. 【Conclusion】Runoff power (ω) is the optimal index for erosion prediction (R²=0.96 for the eluvial horizon and R²=0.91 for the parent material horizon); the erosion of the parent material horizon has a critical slope threshold transition (erosion dominates at 8°, and erosion resistance enhances at ≥15°), and the eluvial horizon is more sensitive to slope gradient changes.