Objective To learn the situation of detention mental of detainees in lockup, so as to carry out targeted psychological health intervention and improve their mental health level, which will facilitate the management and transformation of the detainees. Methods A total of 488 detainees were measured by the self-made detainees' psychological scale. The factors of age, sex, educational background, the types of crime, entry time of the detainees, etc were also investigated. SPSS was used to analyze the score of 10 dimensions (independent, extraversion, delusion, anxiety, depression, impulse, violence, volatility, paranoia and lies). The higher the score, the higher the psychological trait was. Results The scores on gender, education, criminal type and litigation phase were significantly different between different levels. The detainees of primary and under primary education scored highest, female scored significantly higher than male on delusion and violent level (P<0.05). The detainees at remain lockup station scored significantly higher than any other stations on anxiety and depressed level (P<0.05). The highest score of top 3 were duty crime, violent crime and property crime in different types of crime. Conclusion The civil servant in a jail should pay attention on detainees' detention mental, and it's necessary to improve their mental health status and set up the social skills training system.