<p>The large-scale application of recycled aggregate (RA) in geopolymer concrete holds significant potential to promote the utilization of construction solid waste and the development of sustainable building materials. In this study, using nano-SiO₂ and steel fiber as modified materials, sustainable geopolymer recycled aggregate concrete (GRAC) was prepared by replacing natural aggregate with RA. The effects of RA dosage (0-100%) and the modified materials (nano-SiO₂, steel fiber) dosage on mechanical properties and axial compressive stress-strain characteristics of GRAC were systematically analyzed through macro-mechanical tests (compressive, splitting tensile, and flexural strength tests) and microscopic tests (SEM, XRD, and MIP tests). Based on the test results, a segmented compressive constitutive model considering RA dosage was constructed, and it accurately characterizes the nonlinear mechanical response of GRAC. Experimental data revealed deterioration in unmodified GRC mechanical performance compared to the control group at 50% RA dosage. However, the axial compressive strength, splitting tensile and flexural strength increased by 31.5%, 80.49% and 51.84% respectively with addition of 1.5% nano-SiO₂ and 1.5% steel fiber. At the microscopic level, nano-SiO₂ refined the pore structure by filling the pores and promoting the formation of C–S–H gel, while steel fiber restrained crack propagation through a mechanical occlusion effect. Moreover, the synergistic interaction between the two provided a composite reinforcement pathway for GRAC. This study provides valuable data and technical frameworks for the application of GRAC in engineering scenarios, such as prefabricated buildings and green infrastructure.</p>