The interfacial bonding property between carbon fiber laminate (CFL) and concrete is a key issue in the application of RC beams strengthened with CFL. In this paper, fracture mechanics method is used to develop a calculation formula of stress intensity factor for the CFL-concrete interfacial crack. In combination with a series of tests, the interfacial fracture toughness is discussed, and the influencing factors and process of the intermediate crack-induced debonding (IC debonding) are also analyzed. The tests results show that IC debonding is generally induced by the flexural or flexural-shear cracks in the bottom of RC beams around the mid-span, and develop along the interface towards the end of the beam. A method to determine IC debonding derived from theoretic analysis and the tests results demonstrates that the interfacial failure can be effectively avoided by limiting CFL strain in the range of the debonding strain.