Abstract: In order to solve the problems of poor cement projects, such as low durability, low steel slag stacking, and cement production pollution environment, the steel slag is used to replace part of the cement to form a new curing agent, and three kinds of ions which have great influences on the solidified soil erosion in seawater are selected. The strength degradation properties of solidified soil caused by a single ion are thoroughly studied. Through the indoor physical and mechanical tests, the change laws of unconfined compressive strength (UCS) of each group under different seawater and distilled water curing conditions are obtained. The X-ray diffraction (XRD) and electron microscopy (SEM) tests are carried out to obtain the microscopic morphology of the steel slag + cement-solidified soil and the change of its phase with the erosion time. It is found that C₄AF and C₂AF in steel slag can effectively reduce the erosive effects of ions. The effects of three ions on the deterioration of solidified soil are Mg²⁺> Cl^-> SO₄^2-. The Cl^--eroded solidified soil will form CaCl₂ and F's salt, and the non-gelling properties of F's salt will cause deterioration of solidified soil. SO₄^2- reacts with the gelling materials to form gypsum, wollastonite and ettringite. When these materials produce a volume expansion larger than the pore volume, the solidified soil will be cracked. Mg²⁺ erosion will form Mg(OH)₂ precipitate, Mg—S—H and Mg—A—H, and reduce the pH values of the pore solution, causing decomposition of the hydrate gel, and resulting in the deterioration of the strength of the solidified soil. The change of the macroscopic physical and mechanical properties and erosion mechanism are analyzed from the changes of microstructures and phases. This research may provide a theoretical basis for the use of steel slag powder + cement-solidified soft soil in engineering.