Exposure tests were carried out on 300M steel cadmium plated titanium, 300M steel cadmium plated titanium-5228A/CCF300 composite galvanic connectors and 300M steel coating- 5228A/CCF300 composite galvanic connectors at Wanning test station to study the corrosion behavior of galvanic couple connectors composed of 300M steel and 5228A/CCF300 composite. The results showed that after two years of exposure to the marine atmospheric environment, significant galvanic corrosion occurred at the contact area of 300M steel cadmium plated titanium- 5228A/CCF300 composite galvanic connectors. The tensile strength and elongation after fracture decreased by 6.8% and 39.5% due to galvanic corrosion damage. No obvious corrosion was found in 300M steel cadmium plated titanium and 300M steel coating-5228A/CCF300 composite galvanic connectors, and the tensile properties did not show a significant decrease. Hydrogen evolution reaction will occur on the surface of the composite material, and the anode dissolution of Fe and reduction of O will occur in the structural steel when the structural steel and composite material connection structures are used in the marine atmosphere. In order to avoid the occurrence of galvanic corrosion, various protective measures such as surface treatment, organic coating and sealant should be adopted for low-potential structural steel.