Abstract: The mechanical performance of adhesives has significant effects on the interfacial bond behavior of the carbon fiber reinforced polymer (CFRP)-reinforced steel structures. Based on the developed ratio of adhesives, the effects of different nano-SiO₂ on the basic mechanical properties and microstructure of the adhesives after curing at room temperature were analyzed. A total of 31 CFRP plate-steel double lap joint specimens were fabricated, and the experimental researches on bearing capacity, effective bonding length, force transmission mode, and bond-slip constitutive after curing at room temperature were carried out. The influence of the amount of nano-SiO₂ on the interfacial bonding properties of CFRP-steel lap joints was obtained and compared with commonly used adhesives. The results show that with the increase of nano-SiO₂, the stress-strain relationship of the adhesive changes from linear to nonlinear, the strain energy, elongation at break and shear strength are increased by 292.10%, 202.88% and 133.12%, respectively. Microstructural analysis shows that the addition of nano-SiO₂ significantly increases the section roughness forms dense plastic cavities, resulting in more microcracks, and greatly improves the toughness of the adhesive. When the amount of nano-SiO₂ is from 0 to 1wt%, the failure mode changes from interface failure to CFRP plate delamination. The incorporation of nano-SiO₂ can increase the ultimate bearing capacity of the lap test piece (increase by 256.96%) and the effective bond length of the interface (up to 3 times), and improve the strain and interfacial shear stress peak of CFRP surface. The bond-slip curves could be simplified into a bilinear model (triangle-shape) for CFRP-steel joints with 0 and 0.5wt% of the nano-SiO₂, the bond-slip curve could be simplified into a trilinear model (trapezoidal-shape) of CFRP-steel joints with 1wt% of nano-SiO₂, and the bonding interface toughness is greatly improved. The bearing capacity of CFRP-steel interface is affected by the tensile strength and elongation at break of the adhesive. The CFRP-steel lap joint based on nonlinear high-strength adhesive (i.e. adhesive with higher strain energy) has excellent interface performance.