Abstract: People stacked or discharged soda residue into the sea directly, which caused environment pollution. It is imperative to convert alkali slag into geotechnical materials that can be directly used in engineering and realize waste utilization. In this paper, we used the 7-day unconfined compressive strength as an index to determine the optimal ratio of coastal soft soil, alkali slag, cement, quicklime, fly ash and self-made foaming agent. These materials were selected to make solidified lightweight soil with soda residue. We conducted indoor experiment on the new mixture. The results show that the solidified light soil with soda residue has strong structural properties. After the curing age exceeds 28 days, the increase in unconfined compressive strength slows down, and 28 days can be regarded as the critical curing time. The large-deformation mechanical properties of the alkali slag light solidified soil were studied with the ring shear. Under static load and the same normal stress, the peak strength and residual strength of the sample increase with the increase of the density, and the softening phenomenon is also greater obvious. At the same density, with the increase of normal stress, both the peak strength and residual strength increase, but the softening is less obvious. Under dynamic load, when the maximum normal stress is greater than the yield stress of the soil structure, the amplitude, frequency and vibration frequency have a greater impact on the residual strength of the sample. This research provides a reference for the effective treatment of alkali slag and has certain engineering application value.