Research on nature-based solutions (NbSs) for mitigating debris-flow hazards has increased interest in ecogeotechnical systems. Most studies focused on the efficiency of isolated mitigation measures, while the benefits and mechanisms of coordinated approaches remain unclear. Consequently, this study proposed a novel approach to mitigating debris-flow velocity, sediment transport, and energy by utilizing tree-shrub mixedvegetation filter strips (T-SMVFS) along S-shaped flow paths combined with dams. The optimal design determination involved four steps: 1) optimal T-SMVFS row and stem spacings were determined; 2) S-shaped flow path parameters were set based on width ratios; 3) effects of synergistic and individual measures on debris-flow reduction were compared; and 4) a flow velocity reduction equation was constructed, considering the influence of topographic features, vegetation planting patterns, and debris flow properties. Results revealed that a completely covered T-SMVFS with row and stem spacings of 10 and 6 cm in 1/50th scale, respectively, exhibited the best reduction effects with 50% energy reduction, 55% sediment interception, and 53% flow discharge regulation. As the S-shaped flow path width increased, the flow reduction and sediment interception rates decreased sequentially while the transportation capacity increased. Synergistic measures achieved 60% and 70% in energy and sediment interception reductions, respectively, outperforming pure geotechnical and biological measures. Comparisons between different synergistic approaches indicated that a coupled S-shaped vegetation filter strip with a 45% flow path proportion and a beam dam was more effective in reducing debris flow. These findings provide a reference for subsequent optimal mitigation solutions involving NbSs that integrate synergistic eco-geotechnical measures.