This paper studied the main cracking reasons for small and medium-span continuous girder bridge with secondary concreting based on ANSYS. Some prevention measures to concrete crack caused by the inelastic subsidence were also proposed. In considering the global deformation of scaffold-beam, the inelastic deformation of scaffold, the hydration heat of cement, and the characteristics of early-age concrete, influence of inelastic subsidence of support foundation on concrete cracking were analyzed by time-varying transient analysis. It can be concluded that the value of inelastic deformation is the decisive factor for the concrete cracking. Field measurement results of several bridges validate the conclusion.