<p>To investigate the effects of the concrete lattice–vegetation composite revetment on levee slope stability, a new soil–water characteristic curve model was developed that incorporates vegetation root parameters, which incorporated the vertical distribution characteristics of the root system into the porosity calculation for the first time. The model’s validity and accuracy were confirmed through laboratory tests. The proposed model was applied to analyze the stability of the Hongze Lake levee slope, which is protected by the composite revetment of concrete lattice and vegetation. Comparative analyses were conducted on slope displacement, seepage field, factor of safety, and plastic zone distribution under this composite revetment, and the reinforcement mechanisms of the composite revetment was revealed. Additionally, the influences of mean root diameter, root length density, and concrete lattice size on the performance of the composite revetment were examined. The results indicate that vegetations significantly enhanced the slope stability by reducing permeability and improving substrate suction, while concrete lattices primarily reinforced the slope through compression and confinement effects. The composite concrete lattice–vegetation revetment outperforms either component used alone. As root length density increased, the safety factor of the slope gradually rose and eventually stabilized. Conversely, the size of the concrete lattice was inversely proportional to the safety–factor ratio. As lattice size increased, its reinforcement effect diminished. These findings provide valuable insights for the design and parameter optimization of the combined revetment system.</p>