In the scenario of supply-demand imbalance in the subway transportation system, rapid identification and prediction of transportation capacity failure impact propagation and boundaries is the basic information support for coordinated emergency dispatch and command of multi line and multi station subways in large cities. The failure propagation shows the particularity of rapid nonlinear diffusion and directed spread. Aim to meet the high-quality development objectives of smart track, the overall technical route include image feature identification, failure space spread search and information collaborative control. Based on the identification of the spatial structure characteristics that include station, line and network, this paper analyze the characteristics of impact propagation and evolution under the scenario of transport capacity failure, summarizes the impact mode, evolution characteristics and scale distribution of emergencies under the differences of spatial form, structure and environment systematically. Secondly, this paper establish the diffusion boundary, unconventional flow distribution and form calculation model, provides methodology for the construction of rail network emergency response system.