This study investigates the influences of root morphology on the pull-out resistance and shear strength increment of soil-root system for three species of plants commonly used in the soil and water conservation of slope land. The increment of shear strength of soil/root system due to roots can be expressed in terms of increment of cohesion of soil mass. According to the numerical models of soil-root systems of the three plants, one can carry out a series of numerical simulations of pull-out and direct shear tests. The analyses indicate the simulations of ultimate pull-out resistance P_(max) of soil-root system are in good agreement with measurements. Meanwhile, the shear strength increments ΔS_r due to roots of the three plants are different and vary with their specific root morphology. The ΔS_r values increase proportionally as the basal diameter increases, in the order: (Subcostate crape myrtle) > (Cotton rose) > (India-charcoal trema).