Taking Huaijiu River in Huairou District of Beijing as an example, four species of plant materials including Salix aureo-pendula, S. matsudana, Amorpha fruticosa and Vitex negundo var. heterophylla were chosen to take the three point toughness test for the purpose of analysing the flexibility of plant materials, and selecting proper species for degraded riverbank ecological restoration construction. The results showed that the choice of materials for soil bioengineering project based on mechanical analysis of plant was probably a feasible method. Riverbank restoration should give preference to plants with small elastic modulus and big anti-bending force. By analysing the experiment data, we found that anti-bending force was significantly positive with plant diameter; V. negundo var. heterophylla was the plant species which had the biggest elastic modulus compared with others, A. fruticosa was the second. While for S. aureo-pendula and S. matsudana, there was little difference. In respect of anti-bending force, V. negundo var. heterophylla was the biggest while S. matsudana was the smallest. Therefore as a point of view, S. aureo-pendula is superior to S. matsudana as arbor species, and for frutex, A. fruticosa is better than V. negundo var. heterophylla.