The mechanical reinforcement effect of roots on soil shear strength is widely recognized and can be used in slope stability analyses based on the limit equilibrium or finite-element method. Although some advanced root reinforcement models have been proposed to evaluate root cohesion, these models require complicated algorithms and a large quantity of experimental data. This paper provides a simple method to estimate root cohesion based on an uncertainty characterization of a widely used root reinforcement model, the Wu and Waldron model using root cohesion data for four riparian tree species. The capacity of the newly developed method is validated using the root cohesion data for another three species. It is found that the newly developed method has a much higher estimation accuracy of root cohesion than the Wu and Waldron model and has a potential to be applied to other tree species used for soil stabilization projects. The new method provides an alternative option for practitioners to evaluate root cohesion in stability analyses of hillslopes and riverbanks because it is simple and does not need many experiment data.