To address the complex characteristics of high water content and fine-grained composition in Poyang Lake sediment, composite activation technology and microstructure tests were adopted to explore the feasibility of developing solidified composite materials from Poyang Lake sediment. By incorporating industrial waste materials such as mineral powder, along with activators including Na₂SiO₄, Na₂SO₄, Na₂CO₃, and NaOH, the mechanical properties, water-erosion resistance, and freeze-thaw resistance of the solidified sediment were systematically evaluated. Combined with microstructure analysis, the regulatory mechanism of the composite activators on the performance of the solidified sediment was revealed. The results show that the addition of the composite activators promotes the formation of flocculent cementitious substances, effectively fills the pores, enhances the interparticle bonding, and optimizes the microstructure of the solidified sediment, providing a feasible technical path for the resource utilization of Poyang Lake sediment. In particular, the Na+-OH^- dual-drive network formed by Na₂SiO₄ and NaOH significantly promotes the depolymerization-polycondensation reaction of amorphous SiO₂ and Al₂O₃ in the sediment, generating C-A-S-H, N-A-S-H and other alkali gels. The ordered distribution of hydration products significantly increases the 28-day compressive strength of the solidified sediment to 11.61 MPa, a 69.0% increase over the control group, while simultaneously improving water-erosion resistance and freeze-thaw resistance.