The invention discloses a junction temperature testing device and a junction temperature testing method based on the temperature variation of LED (light-emitting diode) relative spectrum, belonging to the field of LED photoelectric detection. The junction temperature testing device based on the temperature variation of the LED relative spectrum comprises a driving power supply, a thermostat, an integrating sphere and a spectrum analyzer; based on the principle of correlation between LED junction temperature and the relative spectrum, on the one hand, the temperature of an LED to be tested is controlled through the thermostat, and the LED to be tested is driven to illuminate by using small current; and on the other hand, the relative spectrum of the LED to be tested is collected through the spectrum analyzer, the relation formula of junction temperature characterization parameter and LED junction temperature is obtained through fitting by adopting the area formed by enclosing of the relative spectrum under different temperatures and a reference relative spectrum as the junction temperature characterization parameter. The invention aims at providing the accurate, reliable, convenient, simple, practical and low-price LED junction temperature testing device and the LED junction temperature testing method.