The present invention relates to a method and a device for transmitting and receiving data by a terminal in a wireless communication system. The present invention can provide a method and a device configured to: generate at least one duplicated data according to the number of multiple radio bearers by using specific data in a first layer of a transmitting device; transmit the specific data and the at least one duplicated data to a receiving device on multiple cells associated with the multiple radio bearers; and when receiving, from the receiving device, an ACK indicating the success of reception of the specific data and the at least one duplicated data, instruct to stop transmission of the specific data and the at least one duplicated data from the first layer to a second layer, wherein the multiple radio bearers are instructed, by a bearer identifier, to transmit the duplicated data.