A study of the capacitance-voltage characteristics of GaN light emitting diode（LED） with a view to reveal its degradation mechanism is presented in this article by forward alternating current small-signal method. Combined with series resistance， ideality factor and tunneling current measurement， the properties of negative capacitance and conductance are discussed. The threshold voltage of negative capacitance during degradation is qualitatively analysed. The decreased negative capacitance during aging may be due to the decrease in the effective acceptor concentration and radiative recombination rate， and the increase of defects and non-radiative recombination centers resulting in the enhanced capture effect of carriers. The tunneling effect leads to the obvious increase of conductance under reversed and low-forward bias voltage. The decreased conductance during aging may be due to the series resistance. On the basis of the capacitance-voltage characteristic， light output， current-voltage curves with the degradation mechanism of LED， the characteristics of negative capacitance and conductance can be used as important evidence for the degradation analysis of LED as proved by experiment and theory.