Abstract: Taking Baoxiang River in Guandu District, Kunming City, Yunnan Province, as the research area, three widely distributed herbaceous plants, Eupatorium adenophorum, Conyza sumatrensis, and Bidens pilosa Linn, were selected for experimental research on mechanical properties of roots and stems, and the internal mechanism of three plants in river slope protection were explored. Based on the analysis of soil properties of the sampling points and herbal attribute comparison of plant samples, plant stem pull-out test, bending test, single tensile test and complex root soil sample direct shear test were carried out. The results showed that the average uplift capacity of the three herbaceous plants arranged in a descending order was Bidens pilosa Linn（34.69 N）, Eupatorium adenophorum（32.50 N）, and Conyza sumatrensis（23.14 N）. The uplift bearing capacity was positively correlated with the quality of root system and above-ground part, and their relationship can be fitted by power function, modified power function and exponential function. The average stem bending strength shown in a descending order was Eupatorium adenophorum（5.18 MPa）, Bidens pilosa Linn（5.01 MPa） and Conyza sumatrensis（2.63 MPa）. The stem diameter had a negative correlation with the bending strength and its relationship can be fitted by an exponential function. The average root tensile stress in descending order was Eupatorium adenophorum（9.26 N）, Conyza sumatrensis（8.54 N） and Bidens pilosa Linn（5.68 N）. The average root tensile strength in descending order was Eupatorium adenophorum（33.87 MPa）, Bidens pilosa Linn（32.74 MPa） and Conyza sumatrensis（22.19 MPa）. The root diameter was positively correlated with the tensile stress, while it was negatively correlated with the tensile strength. Both the two relationships can be fitted by exponential function and power function respectively. The cohesive force of the root-soil complex showed a gradually increasing trend. The increase of Conyza sumatrensis,Eupatorium adenophorum and Bidens pilosa Linn was 90%,120%,and123% respectively,when compared with pure soil. The internal friction angle showed a slowly increasing trend,as Conyza sumatrensis,Eupatorium adenophorum and Bidens pilosa Linn rose by 5%,10%,and 12% respectively. Under the vertical pressures of 100,200,300,and 400 k Pa,the shear strength of the root-soil complexes of the three plants increased significantly when they were compared with pure soil,and the relationship between shear displacement and shear stress was similar to a power function.