The bond between carbon fiber reinforced polymer (CFRP) and concrete is significantly and adversely affected by thermal cycles in air and water. In the present study, the effects of thermal cycles in air or water on the bond performance between CFRP and concrete were examined. A single-lap shear test was adopted to evaluate the performance of the CFRP−concrete bond. A number of 270 thermal cycles in air increased the interfacial fracture energy of the CFRP plate− and CFRP sheet−concrete by 35% and 20%, respectively while 270 thermal cycles in water reduced the interfacial fracture energy of the CFRP plate– and CFRP sheet−concrete by 9% and 46%, respectively. Thermal cycles in water caused the failure mode to change from concrete cohesive failure to primer−concrete interfacial debonding. The failure modes of CFRP−concrete exposed to thermal cycles in air still occurred in concrete. A reduction factor for the CFRP−concrete structure for thermal cycles in water was proposed.