Abstract: The energy radiation phenomenon that is excited when a perturbation source moves along a straight line with a constant velocity in or near an inhomogeneous medium is referred as transition radiation. As a common physical phenomenon, transition radiation is emitted when train induced elastic waves propagate in non-uniform rail infrastructures, which are the inhomogeneous medium. Such non-uniformities of infrastructures are mainly concentrated in transition zones between different track structures, namely between bridge and subgrade, tunnel and bridge or ballast track and ballastless track. In this paper, a two-dimensional plane-stress model is established based on the common configuration of high-speed railway transition zone to investigate the transition radiation of the train-induced elastic wave in transition zones. Two semi-infinite elastic layers with different physical properties are coupled by an inclined interface. The bottom of each layer is fixed and the surface is free. A constant load moves on the free surface with a constant velocity passing through the inclined interface between two layers. The elastic wave field is solved separately in an eigenfield and a free field, respectively. The free field is solved by employing the method of separation of variables. The transition radiation energy flux and the energy flux near the interface are calculated separately with different combinations of load moving velocities and interface inclined angles to analyze the influence of these two factors on the transmission of transition radiation. Results show that the total transition radiation energy increases monotonically and non-linearly with the increase of load moving velocity and interface inclined angle. The transition radiation energy even exceeds the strain energy in the eigenfield when the load velocity reaches 74% of the Rayleigh wave velocity in this case. A larger interface inclined angle (i.e. a shorter transition zone) leads to a larger ratio of the transition radiation energy to eigenfield strain energy.