This paper proposes a design and realization of a network security system based on unidirectional network data control technique and configurable Rijndael AES algorithm.The unidirectional control technique does not process the data downloaded from the server to the client side but checks the data that is uploaded to the server side according to certain security rules, which promises the client side can receive complete and real-time data flow from the server side and prevents key information in private network from being disclosed. Moreover, using the improved AES data encryption standard, messages within the private network are encrypted, which promises the information could be transmitted in security even it is eavesdropped.