Procedural defense is a form of defense proposed by defense counsel based on criminal procedural law, aiming to safeguard litigation rights and supervise the legality of procedures. It is an important component of criminal defense. The illegal evidence exclusion rule is the core content of procedural defense and an important means to achieve judicial justice in criminal cases. This paper, taking the illegal evidence exclusion rule as its core, explores procedural defense from both theoretical and practical perspectives. Firstly, it defines the concept of procedural defense and reviews the development of the illegal evidence exclusion rule, elucidating its current status. Secondly, it categorizes four types of procedural defense: request-based, demand-based, defensive, and remedial, elaborating on their characteristics, application conditions, operational methods, and practical effects. Through a case analysis of the Zhang Guoxi Bribery Case, it demonstrates the specific application of procedural defense in practice. Thirdly, it discusses the value significance of procedural defense, pointing out that procedural defense not only embodies the value of procedural justice but also contributes to achieving the goal of substantive justice. It is of significant theoretical and practical value for safeguarding the litigation rights of defendants, supervising the procedural legality of prosecuting authorities, and promoting the efficiency and fairness of criminal proceedings. Finally, it analyzes the challenges and dilemmas faced by procedural defense in Chinas criminal procedural practice, mainly manifested in the lack of clear and perfect legal basis, the unfair and undemocratic practice environment, and the insufficiently significant and stable practical effects of procedural defense. Some improvement strategies and suggestions are proposed in order to provide reference for the healthy development and wide application of procedural defense.