The invention discloses a local area network (LAN) security management system, and relates to the technical field of network security. The system comprises a client, a monitoring end and a management end; the client is a personal terminal in an LAN; the monitoring end is used for monitoring the security of the LAN, and comprises a monitoring end data transmission module, an external detection module, an activity detection module, a file system detection module, an information acquisition module, an isolating module and an external monitoring module; the management end is used for controlling the access authority and the connection state of the client in the LAN according to the monitoring report sent by the monitoring end, and comprises a management end data transmission module, a judgment and analysis module and a control module. Aiming at the defects that the security measures are imperfect, the sensitive file algorithm is inaccurate, the external detection is not intelligent and the like in the existing LAN security system, the invention provides an improved system, which has perfect security protection measures, sensitive file detection methods and intelligent external detection methods.