Method for channel mode transition in wireless portable internet system

A method for converting a channel mode in a wireless portable Internet system is provided to previously assign radio resources for channel quality information transmission without a special process if a user wants conversion to an AMC(Adaptive Modulation and Coding) channel mode from a diversity channel mode, thereby reducing delay during conversion from the diversity channel mode to the AMC channel mode. A method for converting a channel mode in a wireless portable Internet system comprises the following steps of: transmitting a channel quality information request message for the second channel to a terminal according to a channel mode conversion request message which is transmitted from the terminal and requests conversion from the first channel to the second channel(S100); assigning uplink resources for a response to the message to the terminal if the preset number of frames passes after transmitting the channel quality information request message(S130); and converting a channel for the terminal from the first channel to the second channel according to a response message including the first channel quality information transmitted from the terminal through the uplink resources.