A red mud composite solidification agent composed of industrial waste red mud, calcium carbide slag, and desulfurization gypsum is selected to solidify the low liquid limit silt. The changes of mechanical properties (splitting strength, unconfined compressive strength) and durability (water stability and dry and wet cycle) of solidified silt were investigated. The curing mechanism of red mud composite curing agent was analyzed by SEM and XRD. The experimental results show that the red mud composite solidifying agent can significantly improve the road performance of silt. With the increase of solidifying agent dosage and curing age of solidified soil, the unconfined compressive strength and splitting emphasis of red mud composite solidified soil also increase, and the water stability coefficient can be increased from 69.5% to 82.4%. After 12 wet dry cycles, the strength loss rate of the red mud composite solidified soil reached 35.14%. When the red mud composite curing agent is incorporated into the silt, hydration reaction will occur to form C-S-H and C-A-H with gelling effect, and C-A-H will form ettringite crystals with CaSO4. C-S-H and C-A-H are wrapped and filled with soil particles, and ettringite crystals are interspersed with soil particles to form a whole, effectively improving the performance of red mud composite solidified soil.