[Objective] Severe reservoir sedimentation reduces storage capacity and increases global desilting costs. Traditional disposal of dredged sediments (SD), such as landfilling, occupy land resources and pose ecological risks. This study aims to prepare high-strength geopolymers for high-value utilization of solid wastes. [Methods] Sediment from the Zhongxian section of the Three Gorges Reservoir (D₅₀≈67 μm) as the primary raw material. A ternary system is constructed by incorporating ground granulated blast furnace slag (GGBFS) and Class C Grade II fly ash (FA) to overcome alkali activation constraints, including high SiO₂/Al₂O₃ molar ratio of the sediments and the low reactivity of clay minerals. Specimens were cured under standard conditions for unconfined compressive strength (UCS) measurement. XRD, SEM-EDS, and FTIR characterized the mineral composition, microstructure, and surface functional groups of the ternary geopolymers. Additionally, the leaching concentrations of heavy metals (Cr, As, Cd, Co) from the ternary geopolymers were analyzed using the TCLP method with ICP-MS. [Results] In the SD-GGBFS-FA ternary system, the 28-day UCS ranged 51.9-82.9 MPa. The 1-day UCS increased with GGBFS content, indicated diminishing marginal efficiency of GGBFS reinforcement. For GGBFS and SD fixed at 80% and FA at 20%, increasing GGBFS from 0% to 80% produced 1-day UCS increments of 45.8,26.9,22.9,6.4 MPa, respectively, indicating higher alkali activation efficiency when the GGBFS content was below 40%. XRD patterns revealed a typical amorphous characteristic peak in this specimen in the 28°-30° range. SEM of the B2F8S0 specimen revealed the formation of a continuous and dense C-A-S-H gel, indicating that the co-alkali-activated product of GGBFS and SD was C-A-S-H gel, providing primary mechanical support for the early strength development of the material. FA, rich in components such as hematite and mullite, were hardly susceptible to alkali erosion at early ages. Increasing FA content improved stability of strength at later stages (28 d). At FA content of 40% or more, the UCS from 7 d to 28 d remained stable or even increased slightly, contrasting sharply with the significant strength attenuation of the GGBFS-SD system. XRD patterns showed that for B2S0F8 specimen (20% GGBFS + 80% FA) cured for 28 d, the crystalline peak of limestone (CaO) in FA disappeared, and characteristic diffraction peaks of zeolite-type C-A-S-H minerals emerged. FTIR revealed that, after 28 d of curing, the intensities of Si-O-Si stretching and Si-O bending vibration peaks in the B2S0F8 specimen remained stable, indicating greater geopolymer stability in this system than that in the B2S8F0 system. SEM confirmed that the tacharanite generated in the B2S0F8 system filled the pores, improving the compactness of the matrix and maintaining the long-term strength development. TCLP leaching tests showed that the leaching concentrations of Cd and Co from geopolymers were significantly lower than those from raw materials, indicating that Cd and Co could be stabilized by the geopolymer system. However, Cr and As mainly existed as anionic species, and the leaching concentrations of Cr and As from some samples increased after geopolymerization. [Conclusion] High-calcium GGBFS promotes the dissolution of low-activity aluminosilicate components in reservoir sediment clay minerals and forms dense C-A-S-H structures that enhance structural stability. In high-calcium environments, FA undergoes alkali-activated secondary reactions to generate tacharanite, which fills geopolymer gel pores and maintains long-term strength stability of the GGBFS-FA system. B2S6F2 achieves 72.4 MPa at 28 d, and its heavy metal leaching meets Class Ⅰ criteria. The ternary GGBFS-SD-FA system enables the preparation of environmentally safe, high-strength geopolymers, providing a reference for high-value sediment utilization.