Abstract: This study aims to systematically investigate the shear strength characteristics and freeze-thaw damage mechanism of the root-soil complex in the Shisifenzizi section of the Yellow River embankment in Inner Mongolia, explore the optimal range of root cross-sectional area ratio, and quantitatively analyze the impact of water level changes on the stability of ecological slopes. The objective is to provide a scientific basis for vegetation-based slope stabilization projects in the Inner Mongolia section of the Yellow River, balancing root diameter and quantity in engineering practice to achieve a dual improvement in soil shear strength and freeze-thaw resistance. The study focuses on the embankment of the Xijin section of the Yellow River in Inner Mongolia. Through direct shear tests, freeze-thaw cycle tests, and indoor single-root tensile tests, the effects of water content (w), confining pressure (σ), root diameter (D), root number (N), and root cross-sectional area ratio (RAR) on the shear strength (τ) of slope soil under freeze-thaw conditions were systematically analyzed. The freeze-thaw resistance of each key factor was evaluated, and a slope instability model was established to quantify the impact of water level changes on slope stability. The experimental results indicate that: 1) roots effectively enhance the shear strength of soil by increasing its cohesion (c) and internal friction angle (φ). Compared to bare soil, the bond strength of the root-soil complex increased by 2.77% - 36.2%, and the internal friction angle increased by 7.56% - 26.29%, reflecting the improvement effect of roots on soil mechanical properties. 2) As the number of freeze-thaw cycles (n) increases, the internal friction angle of soil slightly increases, while the shear strength and bond strength significantly decrease. Shear strength, bond strength, and internal friction angle are inversely proportional to water content and directly proportional to confining pressure, revealing the coupling relationship between freeze-thaw damage and water and stress states. 3) As the number of roots, root diameter, and root cross-sectional area ratio increase, shear strength, bond strength, and internal friction angle first increase and then decrease. The optimal range of root cross-sectional area ratio is 0.733% - 0.942%, indicating that there is an optimal root configuration to maximize the reinforcement effect. 4) The sensitivity of each factor to freeze-thaw damage resistance (D_τ) is in the order of confining pressure > root diameter, root number > water content. Freeze-thaw damage resistance decreases with increasing water content and increases with increasing confining pressure. With increasing root diameter and number, it first increases and then decreases. When the root diameter is 4 mm and the number of roots is 7, the freeze-thaw resistance is the best. 5) With the increase in the number of roots, root diameter, and root section ratio, the slope safety factor (K) first increases and then decreases. When the river water level is lower than the groundwater level, the safety factor is greater, indicating that a lower river water level is beneficial to slope stability. Therefore, this study can provide the optimal range of root section ratio for the design of vegetation slope reinforcement projects in the Inner Mongolia section of the Yellow River. During the laying process, the selection of root diameter and number of roots is considered, achieving a bidirectional improvement in shear strength and freeze-thaw resistance, providing a scientific basis for river slope protection in cold regions.