To study the fatigue cracking performance of prestressed reactive powder concrete-normal concrete (RPC-NC) composite beams, four identical model beams were designed and produced by taking the 32-m span T-girder of Chinese railway as the prototype. Static test and constant amplitude fatigue test were carried out on the beams. The number of cracks, crack widths, and crack spacing of the model beams at different cycles were analyzed. Based on the plane-sections hypothesis, the magnified factor of strain in the rebars at crack sections was considered under cyclic loads. Tensile property of RPC and bonding property between RPC and rebar under fatigue loads were discussed, and calculation methods for crack spacing and crack width of RPC-NC composite beams at stable stage of fatigue were deduced based on the bond-slip relationship. For the convenience of design and application, by taking account of the influence of RPC tensile property and the amplification effect caused by cyclic loads, the formula applicable to the crack widths of prestressed RPC-NC composite beams was obtained on the basis of the formula provided by the railway codes of China. The comparison between experimental and calculation results obtained by the two methods show that the maximum crack width of prestressed RPC-NC composite beams can be accurately calculated.