As an important part of the judicial system and the criminal procedure system, criminal defense can be traced back to ancient Rome. The system is rooted in the idea of "respecting human dignity", which emphasizes that criminal suspects and defendants are presumed innocent before being convicted by legal procedures, but enjoy the right of defense and other litigation rights. They can entrust lawyers or other defenders to participate in criminal proceedings, and fully exercise their right of defense to confront the prosecution authorities on an equal footing to safeguard their legitimate rights and interests. This system plays a positive role in the formation of a complete litigation structure, the identification of the truth of the case, the realization of procedural justice and the improvement of litigation efficiency.