Abstract: Solidified miscellaneous fill (S-MF) was fabricated by using broken concrete, plain soil, etc. as raw materials, furthermore, steel slag miscellaneous fill road base material (SS-MF) was prepared by the addition of steel slag as well as slag powder. The orthogonal experiment was used to study the influence of curing agent, cement, crushing material, etc. on the unconfined compressive strength of S-MF and SS-MF, the optimal composition ratio of the two materials was obtained. Based on the S-MF and SS-MF of the optimal composition ratio, unconfined compressive strength, expansion rate and microscopic experiments were carried out to analyze the unconfined compressive strength and expansion rate of materials with different curing ages and their formation mechanism. The result shows that the optimal ratio of S-MF is 50% (mass fraction, the same below) crushed material, 50% plain soil, mixed with 5% cement and 0.018% curing agent, and the optimal ratio of SS-MF is 50% steel slag and 50% miscellaneous fill (m (broken)∶m (plain soil) =6∶4), mixed with 5% cement, 0.018% curing agent and slag powder accounting for 40% of the steel slag content; SS-MF has higher strength compared with S-MF at the same age, and the gap increases with age; The bath expansion rate of 10 d high temperature water of SS-MF at optimal ratio is only 1%, SiO₂ diffraction peak in S-MF diffraction spectrum is higher than that of SS-MF, and the diffraction peak of C—S—H is lower than that of SS-MF; Both SS-MF and S-MF develope from a loose structure to a dense structure with age. In SS-MF, the amount of C—S—H gel produced is more and the structure is denser in SS-MF.