The present specification provides a method for transmitting data in a wireless communication system. More specifically, a method performed by a base station comprises the steps of: scrambling bits constituting at least one codeword by using a scrambling sequence; and transmitting, to a mobile station, data including the scrambled bits on a physical channel, wherein an initial value of the scrambling sequence is determined on the basis of a value calculated by floor calculation of a slot index and the number of slots in a radio frame. Due to these features, the initial value of the scrambling sequence can be kept the same during a specific time interval.