Steel-plastic composite geogrid is a geosynthetic material formed by high-tensile steel wires wrapped in high-density polyethylene to create high-strength strips, arranged in a plane with right angles via ultrasonic welding. It adjusts the tensile strength of the reinforcement strips by varying the aperture diameter and the number of steel wires according to engineering requirements. The steel-plastic reinforced geogrid is compounded through a novel process, with the product's surface pressed to form a regular coarse pattern, which, when laid in the replacement soil layer, withstands immense tensile stress and friction with the backfill. It restricts the shear, lateral extrusion, and bulging of the foundation soil. Due to the high stiffness of the reinforced soil layer, it facilitates the distribution and transmission of upper foundation loads more evenly over the underlying soft soil layer, thereby significantly enhancing the bearing capacity of the foundation. The reinforced soil layer increases the overall stiffness of the soil within the compression zone, benefiting the adjustment of soil deformation. The reinforced soil composite layer formed using steel-plastic reinforced geogrid is a flexible structure that can effectively absorb seismic energy, thus exhibiting excellent seismic performance.