The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing RA procedure in EC mode in a wireless system, the method comprising: selecting a first random access preamble based on a first CE level, when the UE operates in EC mode with the first CE level, transmitting the first random access preamble for a configured number of times, which is determined based on the first CE level, to an eNB, receiving a BI from the eNB within a RAR window associated with the first random access preamble, calculating a BPV based on the received BI and the first CE level, and selecting and transmitting a second random access preamble based on a second CE level, wherein the second random access preamble selection and transmission are delayed by a random backoff time selected according to a uniform distribution between 0 and the calculated BPV.