In the situation that crime is diversified qualitatively and quantitatively, the mutual cooperation system between police and private security is very important to cope with the change of policing environment properly. The primary purpose of this study is to suggest the method to improve the policing service quality of police and advance sound security industry by analyzing the case of close mutual cooperation system between police and private security of USA, which can be called the best country in the field of private security. When considering the cases of USA synthetically, we can know that as the most basic characteristic, the discussion over actual cooperation method is performed on the basis of positive recognition over mutual existence of police or private security. It means that the mutual relationship is based on the basic recognition over partner relationship to meet citizen's desire for safety. While reviewing the cases of USA, Korea shall refer to the fact that social safety activities of advanced countries display effects because of many factors such as various mutual cooperation programs between police and private security, efforts of local government, high quality of private security, reliance of citizen and general understanding of police, private security and citizen to solve crime problem. As shown in the review of USA cases, when considering the fact that the mutual cooperation between police and private security is performed in the level of autonomous police, Korea shall perform autonomous police system to provide better policing service, which is close to citizen.