In order to explore the impact mechanism of the shear resistance of root-soil composite in the Three Gorges Reservoir's water-level fluctuation zone, this study took root-soil composite of Cynodon dactylon as the research object, and used the triaxial test to quantitatively analyze the influence of water content, dry-wet alternate times and root content on the shear resistance of root-soil composite. The results showed that:(1) With the increasing of dry-wet alternate times and water content, the soil shear resistance gradually deteriorated. The shear resistance of the root-soil composite with 13% water content was 0.12%~14.76% and 12.47%~21.14% higher than that of the soil with 18% water content and 23% water content, respectively. The shear resistance of the root-soil composite subjected to 6 and 3 cycles of dry-wet alternation was 6.31%~14.71% and 2.41%~8.19% lower than that subjected to one cycle of dry-wet alternation. (2) Root content could significantly affect the soil shear resistance, and the soil shear resistance with root content of 1.5 mg/cm³ was 0.86%~21.10% higher than that with root content of 0.5 mg/cm³. The internal friction angle increased by 0.09%~16.31%, and the cohesion increased by 2.27%~30.55%. (3) Water content was the dominant factor affecting the soil shear strength. The order of contribution to the shear resistance was water content (61.30%) > dry-wet alternate times (21.17%) > root content (8.28%). This study provided scientific reference for species screening, community construction, ecological construction of soil and water conservation, ecosystem reconstruction, and reservoir management in the water-level fluctuation zone of the Three Gorges Reservoir.