A network security system and method thereof are provided in this disclosure. The network security system includes a server and a client device. The client device is configured for running a firewall according to a first parameter corresponding to at least one setting category, and receiving a second parameters transmitted by the server within a periodic communication interval. The client device further includes a monitoring unit. The monitoring unit is configured for checking automatically whether a setting category of the second parameter matches the at least one setting category during a communication period between the server and the client device; if the setting category of the second parameter matches the at least one setting category, setting up the firewall according to the second parameter; and if the second parameter corresponding to setting category does not match the at least one setting category, omitting the second parameter.