To strengthen the strength and toughness of epoxy resin at the steel-carbon fiber reinforced polymer (CFRP) adhesive interface, polystyrene (PS) microspheres were added to enhance the mechanical properties of epoxy resin. The tensile, bending and impact properties of micron PS toughened epoxy resin under normal temperature curing process were studied. The micromorphology of the tensile cross section of epoxy resin was observed using scanning electron microscope (SEM). The strengthening and toughening mechanism of micron PS particles on epoxy resin was analyzed, and the mechanical property test of the steel-CFRP adhesive interface was carried out. The results show that: the tensile strength, tensile modulus of elasticity, flexural strength, flexural modulus, elongation at break, flexural deflection and impact strength of the adhesives show a tendency to increase and then decrease with the increase of PS dosage when the mass fraction of PS increases from 0% to 5. 00% . When the matrix breaks, the PS particles produce large deformations or hinder the development of microcracks, thereby achieving the purpose of toughening. The larger amount of PS particles will adhere and agglomerate in epoxy resin, resulting in a decrease in the mechanical properties of epoxy resin. As the PS content increases from 0% to 2. 50% , the failure mode of the steel-CFRP bonded specimens gradually transitions from steel plate debonding and adhesive layer cohesive failure to CFRP plate delamination. The tensile strength of the double-lap specimen gradually increases, and the micron PS toughened epoxy resin with mass fraction of 2. 50% shows good mechanical properties in the steel-CFRP adhesive interface.