A method for controlling a security channel for reducing system load by extending the use period of a security association key is provided. In this method, an upper bit initial value of an initialization vector of an encryption algorithm and a using range thereof are shared between a transmitting side and a receiving side when a security channel is created. Then, a secure association is created between a transmitting side and a receiving side by setting an association number, a next packet number which is a lower bit value of an initialization vector, and a secure association key. Afterward, a packet number is modified whenever a frame is transmitted until all of packet numbers are used. When all packet numbers are used, the upper bit value of the initialization vector changes.