Provided is an initial access method for a broadband wireless access system. The initial access method is used between a portable subscriber station (PSS) and a radio access station (RAS) in the broadband wireless access system and includes an authentication operation and a default transport connection setting operation. In the initial access method, default information, which is required to register the PSS and to set default transport connection, is stored in an authentication authorization accounting (AAA) server, the default information is then transmitted to the RAS connected to the PSS in the authentication operation by the AAA server, and when the PSS is registered and the default transport connection is set, a message composed of parameters, which are required to register the PSS containing the default information and to set the default transport connection, is then transmitted to the PSS by the RAS. Accordingly, a simplified initial access procedure is achieved.