To realize the utilization of silt waste from foundation pit excavation, the characteristics of engineering mechanics 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 variation of strength and durability of lime-cement solidified silt. 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 addition of cement and lime; after soaking in water for 5 days with different content, the water stability coefficient of the solidified soil is greater than 0.6. The water stability coefficient increases with the increase of cement content, and increases first and then decreases with the 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 was both 6%. Under this content, the unconfined compressive strength of the improved soil for 28d is 2.05 MPa, and the water stability coefficient after soaking in water for 5 days is 0.76, which shows that the improved soil has good mechanical performance.