Criminal psychology is the study of criminal behavior, motivation, psychological characteristics, as well as crime prevention and governance. It is an intersecting field of psychology, psychology, politics, and many other disciplines. By analyzing the behavior, thoughts, and emotions of criminals, criminal psychologist explored the nature and causes of crime and how to prevent and combat crime. Criminal Psychologists usually need to receive professional training, have deep psychological and sociological knowledge, and be able to use statistics, research methods, data analysis and other skills to conduct criminal psychology research. Their research usually involved the criminal's personality characteristics, psychological state, criminal behavior, motivation, psychological defense mechanism, and so on. Criminal psychologist also had important applications in crime prevention and governance. By studying the criminal's behavior and psychological characteristics, we can predict and prevent the occurrence of crime and formulate effective crime prevention and governance measures. At the same time, criminal psychologist could also provide effective intelligence analysis and decision-making support to the police and judicial departments to help solve cases and fight crime. Criminal psychology is a very important subject that can help us better understand the behavior and motivation of criminals and provide effective support for crime prevention and governance.