1. A method for controlling a multicast and broadcast service (MBS) in a wireless access system, the method performed by a mobile station (MS) and comprising: receiving a first MBS data modulated by a first modulation and coding scheme (MCS) level; transmitting a feedback data through a feedback channel assigned to a contiguous resource unit (CRU), including adjacent subcarriers in consecutive symbols, when the first MBS data does not satisfy a predetermined packet error rate; and receiving a second MBS data modulated by a second MCS level determined based on the feedback data, wherein the MS transmits the feedback data using at least one of orthogonal codes mapped on the CRU, wherein the second MBS data transmitted through a low priority MBS data steam and a high priority MBS data stream embedded within the low priority MBS data stream, and wherein the MS having a channel status value greater than a reference channel status value receives both the low priority MBS data steam and the high priority MBS data stream, and the MS having a channel status value less than or equal to the reference channel status value receives only the high priority MBS data stream.