In the construction of urban rail transit, the project characteristics of electromechanical engineering are multiple specialties, complex systems, many participants, dense interfaces, small space, multiple interleavings, tight schedules and high safety and quality requirements. Therefore, an increasing number of cities have introduced various new technologies into rail transit construction to explore the digital construction of rail transit. This paper introduces the application of BIM technology, 3D scanning, UAV tilt photography, MR, VR, 360-degree panoramic photographyand digital construction platform. Taking themechanical and electrical engineering applications of Chongqing Rail Line 6 Branch Line phase Ⅱ as an example, the digital construction system with BIM+PM+IoT as the core is studied in detail. Through the multi-stage BIM model combined with the digital construction platform, which enables solidified work process, multi-level and multi-departmentalfull participationand the entile process of digital construction implementation process are formulated to realize a new project management mode with digital construction as the core concept. At present, the digital construction platform has accumulated more than 100, 000 pieces of management data, which forms a good regional demonstration and application promotion effect.