Steel fiber-reinforced polymer (FRP) composite bars (SFCBs) can enhance the damage-controllable features of reinforced concrete (RC) structures, offering a potential solution to corrosion issues in conventional RC structures. However, the durability of SFCBs bonded to concrete remains insufficiently studied. Seawater exposure experiments were conducted on SFCBs-concrete specimens with two diameters (12 and 16 mm) at different exposure times (30, 180, and 360 days) and temperatures (23, 40, and 60 °C) in this study. Subsequent pull-out tests were performed to assess long-term bonding behaviors. The results indicate that the hydrolysis of the glass FRP (GFRP) matrix is the primary cause for the reduction in shear capacity of SFCB ribs and the degradation of bond properties between SFCB and concrete. With increasing aging time and temperature, the bond strength of SFCB-concrete gradually decreases. Thicker GFRP layer SFCB-concrete specimens exhibit better bond strength retention rates. Moreover, a predictive model for the bond strength of SFCB-concrete was proposed. As per the model predictions, the bond strength retention after 10 years of seawater immersion is 50% for 12 mm diameter SFCB, while the 16 mm diameter SFCB achieves a retention of 70%. These findings will provide valuable references for the implementation of SFCB-reinforced concrete structures.