Abstract: Objective: Currently, the construction of urban rail transit infrastructure in China is transitioning from the ′constructionoriented′ to the ′construction and management combined ′. The various disciplines of urban rail transit infrastructure have embarked on the construction or research of digital operationmaintenance platforms. Conventional rail state operationmaintenance monitoring and analysis techniques are flawed on multiple levels, thus it is necessary to study automatic monitoring and intelligent diagnosis of rail defect states. Method: A DTSS (digital twin simulation system) based on BIM (building information modeling) is introduced; a digital twin platform is developed for model visualization and data interaction with relevant models; taking Shanghai Rail Transit Line 7 Panguang Road Sta.Liuhang Sta. interval as example, experimental monitoring and digital twin simulation system testing for the status of inservice rail fracture defects are carried out. Result & Conclusion: The monitoring devices of DTSS are arranged in flow line manner, dividing the test rail into multiple intervals for wholeday and realtime monitoring, and transmitting the collected information to DTSS through an internal professional network; the management equipment responsible for monitoring rail fractures in two intervals on both sides of a single sleeper and the monitoring terminals form an assembly of devices. The management equipment and the central server can communicate in multiple ways, and the monitored data is uploaded to the database of DTSS. The average rail deformation calculated by finite element analysis software is approximately 0.51 mm, while the average rail deformation obtained from realtime monitoring is approximately 0.48 mm, with a deformation error of less than 5%, which falls within an acceptable range. This validates the accuracy and reliability of the DTSS platform.