Abstract: An in-situ washing-out test was carried out by the artificial simulation of rainfall to quantitatively investigate the anti-washing-out of a red-bed soft rock slope protected by plants.Some parameters,such as runoff amount,rainfall interception and erosion volume,were measured in the conditions of different rainfall intensities.The results show that a red-bed soft rock slope protected by plants is not washed out nearly when the rain intensity is 20 and 50 mm/h and the duration is 190 and 120 min respectively,and that ecological protections can prevent a red-bed soft rock slope from weathering and disintegrating in a water environment to decrease its washing-out.