To realize the utilization of silt waste from foundation pit excavation, the engineering mechanics characteristics and stability of the Yangtze river floodplain silt subgrade solidified by cement and lime were investigated. A series of laboratory tests including compaction test, unconfined compressive strength test, water stability test and microscopic test were conducted to analyze the strength and durability of lime-cement solidified silt. And the feasibility of using soft soil of Yangtze River floodplain as subgrade filling is demonstrated. The results show that the mechanical properties of silt are greatly improved after the addition of cement and lime; After soaking in water for 5 days with different content, the water stability coefficient of the solidified soil is all greater than 0.6. The water stability coefficient increases with the increase of cement content, and increased first and then decreased with the increase of lime content. Microscopic tests show that the cementitious substances generated by cement and lime in the soil can encapsulate and bond the soil particle. Considering the strength and water stability of the solidified soil, The Yangtze River floodplain silt can be used as subgrade filling after solidification and the optimum percentage of cement and lime is 6% cement and 6% lime. Under this content, the unconfined compressive strength of the improved soil for 28d is 2.05MPa, and the water stability coefficient after 5d immersion is 0.76, which shows that the improved soil has good road performance.