The invention discloses a device and method for calculated the LED junction temperature according to change of spectral distribution. The device comprises a DC power supply, a thermostat, an integrating sphere and a spectrum analyzer, the thermostat is provided with an LED pedestal, the LED pedestal is provided with the integrating sphere, the spectrum analyzer and a computer are arranged outside the integrating sphere, the signal transmission end of the spectrum analyzer is connected with the computer, a probe of the spectrum analyzer reaches the inner wall of the integrating sphere, a DC power supply is connected with an LED light source, the integrating sphere is provided with a hole, the LED light source reaches the inside of the integrating sphere via the hole in the integrating sphere, the DC power supply is also connected with the computer, and the LED light source is placed on the LED pedestal. The method comprises the steps of measuring a vector of a junction temperature scale, measuring a reference curve and measuring the junction temperature to be measured. According to the device and method, only the routine spectrum analyzer and power supply are needed, the method and device are easy to realize, the centroid wavelength, half-height and full-width are easy to measure accurately, the repeatability is high, and thus, an error of the junction temperature is low.