The present invention relates to a wireless access system, and more particularly, to an initial system under a multi-carrier combination condition. A method of for performing an initial access in a base station which supports the multi-band of a terminal according to one embodiment of the present invention comprises the steps of: searching one or more downlink component carriers of the base station; receiving system information including a broadcast channel of a first downlink component carrier from among the searched one or more downlink component carriers and information for indicating one or more uplink component carriers connected to the first downlink component carrier; transmitting a first message to the base station through a first uplink component carrier from among one or more uplink component carriers indicated by the received system information; and receiving a second message including uplink authorization information from the base station through the first downlink component carrier.