The inner mechanisms accounting for the efficiency droop in III-Nitride based LEDs have been investigated extensively. Here we give a brief discussion of the possible mechanisms: defect &dislocations related SRH non-radiative recombination, reduced spontaneous emission, Auger non-radiative recombination, electron leakage, polarization field, current crowding effect. Dislocations do not strongly impact high-current performance; a reduced spontaneous emission reduces internal quantum efficiency (IQE); Defect-assisted and polarization field induced Auger process, electron overflow will strongly influence the droop characteristics at elevated current injection. Current crowding should results to a lower IQE.