Miscellaneous fill, steel slag, and slag powder were mixed to prepare steel slag-miscellaneous fill base material by soil solidification. Firstly, coupling influence test of main materials including steel slag, concrete crushed material and plain soil on the strength of base materials were conducted, regression model was established to obtain optimal mixing ratio. Experimental verification shows that the prediction error was within 2%. Secondly, the orthogonal test was carried out with steel slag, concrete crushing material, cement as well as curing agent as the factors, and the optimal results obtained were basically consistent with the strength coupling influence test. Thus, the optimal mix ratio of steel slag and miscellaneous fill was determined. The test results of the optimal sample showed that the strength increased significantly with age, which presented expansion rate of 1.03% after treatment 30 d high temperature water bath. X-ray diffraction analysis (XRD) and scanning electron microscope (SEM) test results show that SiO₂ in slag powder reacted with f-CaO in steel slag to form hydrated calcium silicate gel (C-S-H). It was also confirmed that the modification of the soil solidification agent to the soil can effectively prevent the expansion of steel slag; C-S-H gel is filled in the space of the broken concrete, steel slag as well as soil particles to increase the compactness of the steel slag-miscellaneous fill base material and thus enhance its strength.