Aiming at YAG white LED generated by blue-light excitation phosphor, a set of junction temperature measurement system based on characteristic spectral parameters is designed by using conventional visible spectroscopy and temperature control system through analyzing spectral trough characteristics. The measurement process is divided into two parts:the measurement of calibration function and the measurement of arbitrary state. Firstly, the relative luminescence spectra at different junction temperature and normal driving current are measured by spectrometer, and then the relative spectral intensity at the spectral trough is analyzed. Considering practicability and cost reduction, normal working current drive is adopted, but the self-heating effect of LED driven by normal working current can not be neglected in the fixed reaction time of spectrometer. Therefore, the selected reference state method is used to make the difference between the relative luminescence spectral intensity at each temperature and the reference state point by point to get the corresponding difference value. At the same time, in order to reduce the temperature deviation introduced by the temperature control system, the corresponding junction temperature difference is also obtained by making the difference between each temperature and the reference temperature. Experiments show that the calibration functions of junction temperature difference and luminescence spectral intensity difference of LED with high and low color temperature have high linearity, and R² is above 0.99. Using the calibration function, the junction temperature of LED can be measured at any state. Finally, the junction temperature data of high and low color temperature LED obtained by the proposed method under different conditions are compared with the measurement results by T3Ster instrument of Mentor Graphics Company. The maximum deviation is 2.82%. Within the acceptable error range, it shows that the proposed method is completely feasible and has certain practical value.