The multidrug resistance of bacteria caused by the abuse of traditional antibiotics poses a great threat to public health, so it is urgent to develop effective antibacterial agents to deal with this dilemma. Biomimetics and nanotechnology are expected to provide new strategies for solving this problem. This study takes inspiration from the adhesive protein properties of mussels to design and synthesise biomimetic polydopamine nanospheres (FeCo@PDA NPs), which have strong adhesion and catalytic Fenton reactive enzyme activity. The antibacterial activity of FeCo@PDA NPs against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) is significantly better than that of traditional antibiotics daptomycin (Dap) and vancomycin (Van). PDA NPs with an intrinsic hierarchical structure have the ability to adhere to bacterial surfaces and improve the loading rate of metal ions Fe2+/Co2+. In addition, due to the dual effects of strong adhesion and Co2+, FeCo@PDA NPs can destroy the bacterial membrane structure and release endogenous hydrogen peroxide, which increases the generation of reactive oxygen species by synergistic catalysis of bimetal ions Fe2+/Co2+ to further kill bacteria thoroughly. The cytotoxicity test results show that FeCo@PDA NPs have good cytocompatibility. The impressive antibacterial properties and good biocompatibility of FeCo@PDA NPs make them a potential antibacterial drug.