The present invention provides a method for determining a modulation and coding scheme (MCS) to be applied to data in a wireless communication system, and a device therefor. Specifically, the method may comprise the steps of: reporting, to a base station, channel state information including a first measurement value related to a channel state between a terminal and the base station; receiving at least one downlink reference signal from the base station; calculating a second measurement value related to the channel state by using the received at least one downlink reference signal; when the second measurement values is equal to or smaller than a preconfigured threshold value in comparison with the first measurement value, transmitting, to the base station, a specific uplink signal requesting a change of an MCS designated to downlink data; and receiving the downlink data, to which the changed MCS has been applied, from the base station.