Abstract: The geology of Shi-Men reservoir watershed is very weak and the slope is very steep.Above 800hectare landslide after Typhoon Aili pounded Taiwan with strong winds and heavy rains.According to vegetation investigation, we choose five of the most important pioneer plants at landslide scars.We investigate the root distribution and evaluate the slope stability.In order to obtain root strength model from pulling resistance and root tensile strength test that analyze the tests' datum by statistical regression.The best estimator for pulling resistance (P) with basal diameter (D) are Taiwan hibiscus:P=5.10D1.49;Subcostate crape myrtle:P=2.82D1.96;Paper mulberry:P=11.75D0.74;Roxburgh sumac:P=12.56D1.32;Indiacharcial trema:P=8.52D1.18.The ability of pulling resistance is Roxburgh sumac>Subcostate crape myrtle>Taiwan hibiscus>Indiacharcial trema>Paper mulberry under fixed root diameter condition.Therefore Roxburgh sumac and Subcostate crape myrtle are really obvious about providing slope stability.