In this study, laboratory tests of the air-booster vacuum preloading method with different air-boosting depths were performed on the Tianjin dredged slurry of high water content. The law of gas migration in soil was used to analyze the reinforcement mechanism and the reinforcement factors. Test results show that the drainage, settlement, dissipation of excess pore water pressure as well as the vane shear strength were significantly improved when air boosting is operated on the lower part of drainage board. In the initial stage of consolidation of the fluid-plastic soil, the injected gas is easy to form bubbles and to move upwards rapidly under the action of buoyancy, which drives the deep soil particles to move upwards and disturbs the soil like stirring, so that the dredged slurry is reinforced more uniformly. As water content of the dredged slurry gradually decreases, the gas in soil will form a closed space with a certain pressure, leading to an increase in pressure between the plastic vertical drain and the gas injection pipe. In the later stage of consolidation, the gas expands in soil, which forms micro-fracture cracks to accelerate the water dissipation in the soil and improves the drainage reinforcement effect.