In order to analyze the thermal characteristic of GaAs-based laser diodes during degradation, aging tests were carried out under the conditions of the constant current stress for808 nm GaAs-based laser diodes. The temperature of active layer and the thermal resistance were investigated by using electrical method. It was found that the temperature of active layer raise with the increase of aging time, while thermal resistance had not changed during aging tests. At the same time, the electrical and optical properties were measured, which indicated that the main reason for degradation was the increase of nonradiative recombination in the active layer. The results show that the degradation of the laser diodes can be observed effectively through thermal property measuring by using electrical method. The experimental results establish the foundation of improving the thermal management technology and thermal properties of laser diodes.