High-Speed Railway(HSR) has entered the era of networked operation. Unpredictable emergencies may disrupt the normal operation of the railway, resulting in train delays. The delays may even cause cascading delays due to the track constraint. This paper proposed a delay propagation model by max-plus algebra, considering the constraint of the HSR network, to predict the spatial-temporal range of cascading delays under emergencies. Moreover, the operation strategy re-management in sections and the re-timing strategy due to the station capacity constraint are studied under emergencies, forming a chain model of emergencies, primary delays, and secondary delays. Simulation results show that the proposed model could accurately predict the secondary delay under different emergencies.