Abstract: The settling column tests and the vacuum preloading model tests are performed on the waste slurry of a construction site in Shanghai and the additive agent slurry. The sediment and turbidity characteristics of slurries with four different agents are studied. The test results show that the turbidity of supernatant decreases after adding agents. The waste slurry mixed with CPAM has the fastest speed in solid-liquid separation and the lowest turbidity of supernatant, and that mixed with PAFC has the slowest speed in solid-liquid separation and the highest turbidity of supernatant. The water yield, water content, particle-size distribution, void ratio and variation of pore-size distribution are studied in the vacuum preloading model tests. The test results show that the small-size particles become larger, and the particles with size larger than 75 mm increase by 13.01% after adding agents and increase to 23.68% after vacuum preloading. The results of mercury intrusion porosimetry tests show exactly the process of pore change during adding of agents and vacuum preloading. The water velocity of slurry with common vacuum preloading decreases quickly after starting of vacuum preloading, and drain channels are clogged by particles. The water velocity of slurry with additive agents combined with vacuum preloading decreases slowly and it exhibits great anti-clogging effect of additive agents. The water yield of slurry with additive agents combined with vacuum preloading is nine times larger than that with common vacuum preloading. Finally, the reasons for anti-clogging effect of additive agent combined with vacuum preloading are explained by the variation of particle size, loss of small particles, and reduction of flow resistance.