Abstract: Train virtual formation is a new type of train flexible formation technology based on train-to-train communication, and has gradually become a research hotspot in the industry. Flexible train formation can effectively solve the problem of uneven spatial and temporal distribution of rail transit passenger flow, it is also of great significance in terms of energy saving and consumption reduction. In this paper, the capacity bottleneck problem of rail transportation network and its demand for flexible train formation are expounded, the practical application cases and characteristics of flexible train formation at home and abroad are compared. With an analysis of the technical concept of virtual formation, the coupling and decoupling processes of virtual train formation are studied. On this basis, the key technical support (including train active real-time positioning with high accuracy and low-latency, highly reliable vehicle-to-vehicle wireless communication, etc.) and core technologies (including the optimization of highly intelligent, adaptive train formation cooperation, the multi-vehicle collaborative control and protection with high safety and strong resilience) required for the application of train virtual formation are proposed.