The present invention relates to 5G or pre-5G communication system for supporting a higher data transmission rate after 4G communication system such as LTE. The present invention provides a method and a device for executing a hybrid automatic repeat request (HARQ) through a channel in an unlicensed frequency band. More particularly, a method for executing a HARQ through a channel in an unlicensed frequency band in a terminal of a communication system comprises the procedures of: requesting uplink scheduling; if a first uplink (UL) grant with respect to the scheduling request is received, sensing whether or not a channel is clear; transmitting first uplink data on the basis of whether or not the channel is clear; if negative acknowledge (NACK) with respect to the first uplink grant and a second uplink grant are received, sensing whether or not the channel is clear; and transmitting second uplink data and an indicator, which indicates whether or not the second uplink data transmission is a retransmission, on the basis of whether or not the channel is clear, wherein the indicator, which indicates for retransmission, is determined on the basis of a reference signal (RS) detection failure indicator, of a base station, which is transmitted from the base station together with the second uplink grant.