The present invention relates to a wireless communication system. More specifically, the present invention relates to a method for acquiring, by a first user equipment (UE) in a coverage of a first cell, synchronization in a wireless communication system, the method comprising: receiving a message for a sidelink resource configuration from a second cell through the second UE in a coverage of the second cell; if a channel quality of the second cell is less than a predetermined threshold, selecting the first cell as a synchronization reference cell; and transmitting a sidelink data to the second UE using the sidelink resource configuration based on the synchronization acquired from a synchronization signal of the first cell.