The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting a power status reporting in a carrier aggregation with at least one SCell operating in an unlicensed spectrum, the method comprising: receiving an uplink grant to transmit data on a cell from an eNB; determining drop of the data transmission on the uplink grant; generating information including an indicator indicating that the data transmission is dropped; and transmitting the information to the eNB.