Abstract: To investigate the effect of long-term marine atmosphere on the bond behaviour of carbon fibre reinforced polymer (CFRP)-steel interface, 36 CFRP-steel plate double-lap joint specimens were designed and fabri-cated. A salt spray box with a salt spray deposition volume of 1-2 mL/80 (cm²·h) was used to simulate the marine atmospheric environment. Fatigue and static tensile tests were carried out successively. The effects of environmental exposure time (30, 180, 360 days), long-term sustained load and silane surface treatment on the failure mode and ultimate bearing capacity of the CFRP-steel interface were analyzed. The results show that the failure mode of CFRP-steel interface gradually changes from cohesive failure and CFRP delamination to steel-adhesive interfacial debonding with the increase of exposure time to marine atmosphere. The long-term marine atmosphere effects cause significant degradation of the CFRP-steel interface bond performance, and the ultimate bearing capacity decreases by a maximum of 15.72% after 360 days of exposure. Silane surface treatment has little effect on improving the durability of CFRP-steel interface. The sustained load causes the ultimate bearing capacity to decrease by 18.39% under the short-term environmental action (30 days) while having little effect on the long-term environmental action. The high stress preload fatigue resulted in a maximum decrease of 26.6% in the ultimate bearing capacity. The Hart-Smith model was used to calculate the ultimate bearing capacity of the CFRP-steel interface, and it is found that the error between the predicted and experimental values of ultimate bearing capacity after long-term environmental action exceeds 30%. After considering the influence of failure mode change on the ultimate bearing capacity, the error is reduced to a maximum of 14.04%.