The fatigue performance and durability of the reinforced concrete (RC) beams strengthened with fibre reinforced polymer (FRP) laminates is an advanced research topic in civil engineering. The crack propagation life is the dominant part of the whole fatigue life of the cracked RC members strengthened with FRP laminates under cyclic loads. In this paper, a theoretical and experimental study was conducted to investigate the rule of the fatigue crack propagation of the RC beams strengthened with carbon FRP (CFRP) under constant cyclic bending load. A total of 5 RC beams with sizes 1850×100×200mm strengthened with CFRP were tested. The results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation (Phase I), stable propagation and then rest (Phase II) and unstable propagation (Phase III). In accordance with Paris-Erdogan Law, a semi-empirical equation was developed to predict the crack propagation rate. The empirical coefficients of the equation were obtained from the fatigue test results. To validate this equation, the predicted fatigue life of crack propagation calculated by it is compared with the data obtained from tests. It shows the agreement is good.