The steel slag-miscellaneous fill base was prepared by mixing steel slag, slag micropowder and waste concrete debris, and its performance was studied. The volume stability test shows that the slag micropowder has obvious anti-expansion effect. The 10 d high temperature water bath expansion rate of the specimen mixed with 50% (mass fraction, the same below) steel slag, 50% miscellaneous fill and 30% slag micropowder is only 1.32%, while the 3~5 d expansion rate of the specimen without slag micropowder exceeds the 2% limit. The orthogonal test of 7 d unconfined compressive strength and 28 d splitting strength shows that the order of influencing factors of 7 d unconfined compressive strength and 28 d splitting strength is steel slag, cement content, concrete debris proportion and soil stabilizer. The maximum values of 7 d unconfined compressive strength and 28 d splitting strength in each group are 12.41 MPa and 2.24 MPa, respectively. The optimum ratio of steel slag-miscellaneous fill base is 50% steel slag, 50% miscellaneous fill (m(concrete debris)∶m(plain soil)=6∶4), adding 40% slag powder, 5% cement and 0.018% stabilizer. At this time, the specimen has good water stability. The test of strength influencing factors show that slag micropowder has the greatest influence on the increase of specimen strength. X-ray diffraction and scanning electron microscope analysis show that f-CaO in steel slag is effectively digested under the action of slag micropowder and soil stabilizer. The dense package of aggregates, concrete particles and steel slag particles prevents the volatilization of internal water and the invasion of external free water, which not only ensures the strength of steel slag-miscellaneous fill base, but also effectively inhibits the expansion.