The robustness of transportation networks under emergency events is a key factor in assessing the resilience of urban public transportation systems. To study the emergency response capabilities and resilience performance of complex urban transportation systems during emergency events, this study takes the central urban area of Chongqing as the study region and constructs a bus-metro multilayer transportation network model based on complex network theory to evaluate the robustness and emergency response capabilities of the urban transportation system under different shock modes. Through simulation analysis, the study delves into the catastrophic failure mechanisms and resilience trends of the two-layer network, and investigates the emergency coordination capabilities of metro and bus lines. In response to the vulnerability of single networks in current urban transportation systems during emergencies, an improved load-capacity model is proposed and used to analyze the network resilience under different attack modes. The study results show that: (1) The two-layer network exhibits a slower decline in network efficiency under both shock modes, with its redundancy and multi-path characteristics effectively mitigating the collapse process; (2) In the cascading failure process, the robustness of the two-layer network is consistently superior to that of single bus and subway networks, and the cascading failure caused by the failure of important stations has a more significant impact on network connectivity and efficiency; (3) The two-layer network is more effective in maintaining network connectivity and operational efficiency, especially when facing unexpected events, demonstrating stronger adaptive capacity and robustness. It can effectively share the load, alleviate congestion in single networks, and improve emergency handling efficiency.