Without a safe and orderly condition in prison, all activities, both coaching, care, and guidance, will not run smoothly. There are frequent violations of discipline committed by convicts, such as mobile phones, extortion, and drugs (halinar) in Purwokerto prison, so the authors take the formulation of the problem of how to use the concept of Crime Prevention Through Environment Design (CPTED) as a security strategy to prevent convict violations in Purwokerto Prison and what are the obstacles in implementing it. This thesis aims to find out how the CPTED concept is applied and its constraints in Purwokerto prison. This study uses the CPTED theory from C. Ray Jeffery with a descriptive qualitative approach and data collection from interviews, observation, and literature studies. There are six principles to apply the CPTED concept: territoriality, surveillance, access control, target hardening, image and management, and activity control. In its implementation, Purwokerto Prison also encountered obstacles such as the quality and quantity of human resources, differences in theory and its application in the field, unfavorable geographical location, ineffectiveness of CCTV, and regular patterns of officers that inmates can read.