Investigating the relationship between soil-water characteristic curve (SWCC) and shear strength of root-soil composites is expected to provide a scientific basis for revealing the strengthening mechanism of purple-soiled root-soil composites and maintaining the stability of soil bunds. The root-soil composites of herbaceous plants on the soil bunds of typical purple-soiled sloping farmlands in the Three Gorges Reservoir region was selected as the research object, and the effect of matrix suction on the shear strength of root-soil composites was constructed by using Hyprop2 soil moisture characteristic curve measuring instrument, filter paper method combined with the direct shear test. Major findings were: (1) SWCC of the root-soil composites could be divided into boundary effect zone, transition zone, and unsaturated residual zone, and the F-X model fitted best among the three commonly used models (B-C, VG, F-X). The saturated water content, air intake suction, residual water content, and suction at the same volumetric water content of the root-soil composites were all higher than those of the plain soil. (2) The cohesion of the root-soil composites first increased and then decreased with the decreasing volumetric moisture content, and the maximum cohesion of 51.25 kPa in the test range occurred at a volumetric moisture content of about 23%. At the same time, the angle of internal friction increased linearly. The cohesion of root-soil composites increased by 50% compared with plain soil at the same volumetric water content, and the internal friction angle was not greatly enhanced. (3) The enhancement effect of matrix suction on the shear strength of root-soil composites and its parameters had a stage-specific characteristic, and the critical suction value of each stage was consistent with the SWCC. The shear strength of soil in the transition zone(where the matrix suction was 3~500 kPa) was most obviously improved. After entering the unsaturated residual zone (matrix suction was greater than 500 kPa), the shear strength of soil increased at a slower rate due to the decrease of cohesion. In addition, the shear strength of the root-soil composites raised with increasing matrix suction to a greater extent than that of the plain soil. Establishing the relationship between SWCC and shear strength of the root-soil composites of purple-soiled bunds could estimate the shear strength of soil bunds under actual working conditions, which provides an important theoretical support for the construction, maintenance and management of slope cultivated land and the erosion control of slope cultivated land.