Abstract: Background In recent years, under the combined effects of extreme weather and human activities, the banks of the Fen River have faced severe soil erosion and functional degradation. The probability of landslides and soil erosion occurring on these slopes during rainfall or river scouring has increased. Planting suitable soil-conserving plants on the slopes is an important biological measure that can effectively address the issue and enhance the stability of the riverbanks. Methods In the upper and middle reaches of the Fen River, rootless soil of different depths and typical riparian herbaceous plants were selected as research objects, and through root morphology survey and important value analysis, four plants with higher dominance were selected for root tensile testing, Root cohesion was quantified based on the Wu model. Combined with soil direct shear test results, the slope stability safety factor was calculated using the rigid body limit equilibrium method to analyze slope stability. Results The results showed that: 1) Combining the results of the root morphology survey and the calculation of the importance value, the dominant plants in the upper riparian zone were Phragmites australis, Humulus scandens and Eleusine indica, and in the middle reaches were Lolium perenne and Phragmites australis; 2) The root tensile force of herbaceous plants tended to increase as a power function with increasing diameter, and the root tensile strength tended to decrease as a power function with increasing diameter. The average tensile force of the root system was in the order of midstream P. australis (114.72 N) > upstream P. australis (94.43 N) > H. scandens (13.87 N) > L. perenne (5.42 N) > E. indica (4.26 N), and the average tensile strength was in the order of H. scandens (264.82 MPa) > E. indica (210.97 MPa) > L. perenne (81.98 MPa) > midstream P. australis (14.23 MPa) > upstream P. australis (13.54 MPa); 3) For both shallow and deep soils in riverbanks, herbaceous plants other than P. australis exhibit varying degrees of root cohesion; 4) The slope safety factors of the midstream and upstream slopes of the Fen River bank were improved after simulating the cover of dominant herbaceous plants, and the slopes reached a stable state. In the midstream, L. perenne had the best effect on enhancing slope stability; in the upstream, E.indica had the strongest effect on enhancing shallow slope stability, and P. australis had the strongest effect on enhancing deeper slope stability. Conclusions In the ecological measures for Fen River slope protection, the combination of oxalis and reed planting or more ryegrass planting can be selected according to the slope geography, and the results of the study can be used as a reference for the biological slope protection measures in the riparian zone.