Peroxides are widely used in environmental applications due to their strong oxidizing properties, however, traditional activation methods often face challenges such as uncontrolled reactive oxygen species (ROS) generation and high energy barriers. Recent advancements in spin state regulation provide a promising alternative to enhance the efficiency of peroxide activation. This review provides an overview of spin fundamentals and discusses the key factors affecting spin state in catalytic materials, including crystal field configuration, ligand environment, and valence changes. Subsequently, the role of electron spin state in peroxide activation is comprehensively analyzed, with a focus on how spin state regulation can tune adsorption energy, lower energy barriers, facilitate electron transfer between transition metals and peroxides, and promote selective ROS generation. Finally, this review briefly outlines the practical applications of peroxide activation in water treatment and concludes with a summary and perspectives on future research directions. This review aims to provide a comprehensive perspective on the role of spin state regulation in advancing peroxide activation strategies.