The geogrid reinforced waste steel slag is a new technique for foundation backfill proposed by authors. The shear strength characteristics of geogrid reinforced waste steel slag were studied through triaxial consolidation and drainage tests. Taking basalt fiber geogrid and abandoned steel slags from Jiangsu Yonggang Company as an example, the stress-strain characteristics of geogrid reinforced waste steel slag of different relative densities, with different geogrid layers and under different confining pressure were analyzed. The reinforced effect of different reinforcement schemes was analyzed and the shear strength characteristics of geogrid reinforced waste steel slag were compared with traditional soil, special soil, and geogrid or lattice reinforced special soil studied by predecessors. It can be seen that the cohesive strength is far greater for geogrid reinforced steel slag than traditional soil under various working conditions. The internal friction strength is also higher, reaching the friction strength of sand. The cohesive strength of geogrid reinforced steel slag is lower than that of loess and expansive soil under each working condition, but the internal friction strength is higher. Therefore, it can be concluded that the shear strength of geogrid reinforced steel slag is higher than that of traditional soil, special soil, geogrid reinforced special soil and geocell-reinforced reinforced special soil under many conditions. Thus, the geogrid reinforced steel slag could be used in soft soil foundation treatment or reinforced engineering backfill.