<p>The utilization of solid waste is of great significance in ensuring ecological construction. To maximize the consumption of solid waste (alkali slag) and achieve green ground reinforcement, a large amount of alkali residue (as an additive) is mixed with dredged sludge to form a large-scale and widely distributed subgrade filling material. However, the chemical modification mechanism and dynamic long-term deformation characteristics of dredged sludge improved by alkali slag are still unclear. A series of scanning electron microscope tests and cyclic triaxial tests under various confining pressures and cyclic stress ratios of the dredged sludge with different alkali slag content were carried out. Scanning electron microscope tests present alkali slag promotes the aggregation of small particles into large particles, the pores of the soil become smaller, aggregates increase, and the pore structure becomes denser. In cyclic triaxial tests, the dynamic resilience modulus, damping ratio, and cumulative plastic strain of soil samples were compared and analyzed. The results showed when the alkali slag content was 20%, the soil samples had the best dynamic long-term deformation characteristics. As the confining pressure increases and the cyclic stress ratio decreases, the damping ratio and dynamic resilience modulus of the dredged sludge improved by alkali slag show an increasing trend, while the cumulative plastic strain shows a decreasing trend. Based on the Monismith power function model, alkali slag content and the cyclic stress ratios are introduced to establish the axial cumulative plastic strain prediction equation, which is demonstrated effectiveness by comparing the results of other scholars. This paper is designed to present the dynamic long-term deformation characteristics of dredged sludge improved by alkali slag and elucidate the microscopic mechanism of alkali slag’s chemical modification on dredged sludge.</p>