With the continuous development of the economy and the expansion of urban areas, it is imperative to promote the resource utilization and recycling of construction waste. As the crushed material obtained from the screening of construction waste, recycled concrete aggregate has broad application prospects. This study focuses on four different particle size ranges of recycled concrete aggregate and investigates the interface shear characteristics between recycled concrete aggregate and bi-axial polypropylene geogrid using large-scale indoor direct shear tests. The results showed that as the aperture ratio decreases, the peak shear stress and residual shear stress at the shear interface increase, and the peak shear stress occurs at a later stage. As the aperture ratio decreases, the peak apparent cohesion and residual apparent cohesion gradually increase, and the peak internal friction angle and residual internal friction angle also increase. The addition of geogrid effectively reduces the occurrence of shear dilation at the interface. By introducing the Kalhaway constitutive equation, the expression for shear stiffness is derived through linear and logarithmic fitting, and the shear stiffness corresponding to the stress state (σn,τ) is obtained. This study reveals the shear mechanism of the interface between recycled concrete aggregate and bi-axial polypropylene geogrid, and the determination of shear stiffness is of great significance in engineering for evaluating deformation mechanisms and stability.