Abstract: As power and natural gas systems become more closely interdependent, the risk of fault propagation across these systems during extreme disasters is significantly heightened, potentially leading to an expanded scope of power outages. The fault propagation analysis in the interdependent power and natural gas systems is foundational for understanding the evolutionary mechanisms and developing appropriate mitigation strategies. Firstly, with the Texas blackout event as the background, how faults propagate across energy systems under extreme disaster conditions is analyzed, and the key considerations to be emphasized in the analysis are identified. Secondly, the fault propagation process is analyzed from three perspectives: coupled modeling, co-simulation, and implementation methods. Emphasis is placed on the time scale and modeling requirements, incorporating models of power systems, natural gas systems, and coupled components suitable for analyzing disaster propagation. A co-simulation method that integrates time-driven and event-driven methods is designed and facilitated by customized interfaces for exchanging information between simulation software. This method enables the spatiotemporal interaction of simulation data between the power and natural gas systems on their respective platforms, providing an intuitive representation of the fault propagation process. Lastly, through a case study of an integrated power and natural gas system, the fault propagation process and fault defense measures under extreme cold disasters were examined, thereby validating the effectiveness of the proposed method.