The fatigue experiments of carbon fiber reinforced polymer （CFRP） laminates-steel double lap joint specimens were carried out. Considering the effects of load levels， the fatigue behaviors of the interface were analyzed. Meantime， the applicability of the mean stress-number of cycle（S-N） curve and designed S-N curve based on mean or local bond stress range were compared. The results show that the main failure modes of specimens under fatigue load are steel-adhesive interface debonding or the mixed mode of steel-adhesive and CFRP laminate-adhesive interface debonding. The slope variation trend of load-displacement curves at different load levels is roughly the same. The interface damage starts from the load end with larger interfacial bond stress and gradually extends to the free end. After expanding to a certain extent， the interface suddenly fails. Using a power function formula to predict fatigue life of specimen， the fitting superiority of S-N curve based on mean bond stress range is more significant， and the fatigue limit is 1.88 MPa. Finally， the designed S-N curve with 95% probability is given.