Abstract: The biotechnical slope protection is a new method to protect slopes, which helps to prevent and control landslide. However, the vegetation roots can increase the permeability and pore water pressure of soils, which in turn decrease the shear strength of soils under rainfall conditions. On the other hand, the roots can be viewed as fibers in the soils and may increase the strength of soils. The controversial effect of roots on the soils remains unclear. The hydraulic and mechanical characteristics are analyzed through field monitoring combined with triaxial compression tests. Firstly, three soil regions (with Vetiver grass, with Bermuda grass and bare soil) are prepared in the field. The monitoring of volumetric water content and matric suction begins after these regions experience natural drying-wetting cycles for one year and a half. The unsaturated permeability functions for the three soils are calculated using the monitored data. Secondly, the soils are sampled from the field and used to conduct trixial tests in lab. The stress-strain curves for the soils with Vetiver roots, the soils with Bermuda, the bare soils and the compacted soils are investigated. The cohesions and friction angles of soils are obtained. The results may provide necessary data in the stability analysis of ecological slopes.