1. A method for transmitting data in a wireless access system, the method comprising: receiving a first sequence including a first CRC; obtaining a number C of code blocks by considering a size L of second CRCs to be attached, the number C being determined based on a size B of the first sequence, a maximum size Z of code blocks, and the size L of the second CRCs; obtaining a size B′ of a modified first sequence by using the number C, the size B and the size L; obtaining one or more sizes of each of the code blocks based on the size B′ and the number C; segmenting the first sequence into second sequences based on the number C and the one or more sizes of the code blocks; generating each of the second CRCs by using each of the second sequences, wherein a size of each of the second sequences corresponds to a bit size except for the size L of the second CRCs from each of the one or more sizes of the code blocks; attaching each of the second CRCs to each of the second sequences; and transmitting the data using the code blocks.