This book systematically explains the theoretical framework of Prognostics and Health Management (PHM) for traction power substations in high-speed railways, focusing on PHM concepts and development. It provides an overview of fault diagnosis and prediction for these substations, complemented by practical examples. The integration of equipment service performance, degradation patterns, fault evolution processes, and intelligent early warning mechanisms is discussed to conduct health assessments of traction power substations. Reliability and risk assessments are conducted considering operational characteristics, relay protection, and multi-factor integration, followed by case analyses. Furthermore, maintenance decision-making and optimization research are explored, encompassing degradation modeling, fault prediction, risk assessment, and multi-attribute decision-making approaches. By incorporating PHM technology into high-speed railway traction power substations, it leverages existing monitoring data while integrating and processing multi-source system information. This enables timely prediction and warning of system and equipment failures, aiding operators in maintaining the system health and conducting reliability assessments. This ensures that the traction power supply system operates efficiently, minimizing failures. Corresponding maintenance strategies are formulated based on evaluation results, enhancing the safe and reliable operation of the system in terms of various aspects such as reliability and economy, etc.