At present, China railway development is in a critical period of strategic opportunities. Smart railway have become an important development direction. Digital twins is an important mean for smart railway construction, which can solve the problem of information and physical integration and realize the application of smart railway. Therefore, based on the analysis of the relationship between digital twins and smart railway, this paper proposes a railway digital twin model based on the five-dimensional digital twin model, and explores the description framework of the railway twin system and the railway digital twin architecture, which provides a certain reference for the application of digital twins in the railway field.