Under the guidance of the national "new infrastructure construction" strategy for the construction of digital twin cities, China's urban rail transit engineering, as an important part of urban public infrastructure, has entered a new development period. By constructing a digital twin system, the intelligent progress of the whole life cycle of urban rail transit engineering will be accelerated. This paper mainly studies some key areas of constructing a digital twin standard system for urban rail transit. Firstly, the purpose and significance of constructing the digital twin standard system for urban rail transit as well as the current status of standardization for digital twins in urban rail transit are elaborated, and some key principles of constructing the standard system are analyzed. Secondly, a digital twin standard system framework for urban rail transit is established based on the manufacturing industry's current digital twin model architecture and technical system. Finally, a detailed analysis is conducted on the constructing basis and schemes of technical standards for physical entities, virtual entities, platforms and services, connections and integrations based on the current domestic rail transit standards, which is expected to promote the comprehensive applications of digital twin technology in China's urban rail transit field.