Abstract: Background To elucidate the influence of vegetation on the initiation of particle scouring on loose slopes, laboratory flume scour model tests were conducted based on the Baicaopo Photovoltaic Power Station project in Yanyuan County, Sichuan Province. Methods Uniform cylindrical steel rods were employed to simulate rigid vegetation. Loose granular slope models with varying inclines (5°, 10°, 15°) were constructed. Conditions including vegetation height, density, and particle size were systematically varied to simulate slope scouring processes under rainfall runoff conditions. High-speed cameras monitored particle movement on the slope surface to determine the critical runoff depth at which particles exhibited significant displacement. Results Experimental findings indicate that increasing slope gradient significantly reduces the critical runoff depth required to initiate particle scouring, exhibiting a non-linear relationship. Elevating vegetation height increases this critical depth, though this effect diminishes with steeper slopes: at 5° gradient, raising vegetation height from 3 cm to 5 cm increases the critical depth by 0.022 m; while at 10° and 15° slopes, this increment was 0.012 m and 0.010 m respectively. Particle size exerted relatively limited influence on critical flow depth; at identical slopes, the difference in critical flow depth between 4.5 mm and 7.5 mm particles did not exceed 0.006 cm, indicating particle stability approached the initiation threshold under smaller grain sizes. As vegetation density increases, runoff energy dissipation intensifies, leading to an overall rise in the critical runoff depth required to initiate particle scouring. Conclusions Slope gradient is the dominant factor controlling particle scour initiation on loose slopes; its increase diminishes the protective effects of vegetation and particle size. These findings provide experimental evidence for soil conservation and slope scour prevention on non-cohesive slopes under rigid vegetation cover conditions.