In order to promote the recycling of industrial waste and effectively improve the utilization rate of engineering waste soil, three common industrial solid wastes, such as blast furnace slag, steel slag and phosphogypsum, were combined with cement, and polycarboxylic acid water reducing agent was used to solidify the project abandoned soil. Through D-optimal mixing test, the optimal mixing ratio of the curing agent was determined as: blast furnace slag∶ steel slag∶ phosphogypsum∶ cement∶ polycarboxylic acid = 59.9∶5∶ 20∶ 15∶ 0.1. Under this formula, the 7 d unconfined compressive strength of the solidified soil reached 5 583 kPa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were used to analyze the microstructure of the soil solidified by the new curing agent. The results show that a large number of filaments, needles and flocculents formed in the solidified soil made the pores smaller and the soil structure more compact. The research results can not only provide reference for the resource treatment of industrial wastes and construction spoil, but also provide certain theoretical guidance for the secondary utilization of engineering waste soil, which has considerable engineering applicability.