The slag from the furnace bottom in Shandong province is mixed with Portland cement and limestone powder to prepare composite powder. Carbonate was used as the activator, and the coal-fired slag-based foam lightweight soil road materials are prepared by physical foaming method. The influence of wet volume-weight of slag base lightweight soil materials on mechanical properties, working performance, defoaming rate and porosity was studied. The results show that the unconfined compressive strength of slag-based lightweight soil decreases greatly with the decrease of wet unit weight, and the flowability decreases linearly with the increase of foam rate. The defoaming rate of lightweight soil has little change in the range of 650~750kg/m3 wet volume-weight. Considering various performance factors, lightweight soil with 650 kg/m3, Slag accounts for 50%, cement for 40%, limestone powder for 10%, and the activator admixture dosage for 4% can be prepared, which can better meet the workability of foamed lightweight soil, and the defoaming rate is low. 3d strength of sample can reach 0.79 MPa and 28d strength can reach 1.63 MPa.