Disclosed is a resource allocating method of a LTE-advanced based D2D communications system including a plurality of D2D terminals, the method comprising: by the D2D terminals, requesting a base station to allocate a licensed band and searching for a spectrum for usable non-licensed bands; generating a D2D communications link by using a resource of the licensed band that is allocated from the base station; calculating a signal to interference and noise ratio (SINR) of the D2D communications link; selecting at least one of resources of the searched non-licensed band when the signal to interference and noise ratio (SINR) is smaller than a threshold value; and performing D2D communications by using a resource of the selected non-licensed band.