Thermal characteristics of ligh t emitting diode (LED) devices direct ly affect their performance, such as luminous efficiency,emission wavelength,reliability ,and lifetime. T hermal resis tance is a c omprehensive param eter reflecting the heat transfer capabilit y of the device,so it is particularly important to accurately measure the t hermal resis tance . In this paper,relationship s between thermal resistance and luminous flux and electrical power are simplified based on the photo - electro - thermal theory,in which t he photometric,electric al,and thermal features of LED s are highly dependent on one another. A new method using the optical ,e lectrical and temperature characteristics of the LED is proposed to measure the thermal resistance. T he calculation of thermal resistance of the LED utili zes the reduct ion rate of luminous efficacy with the increasing temperature k e , heat dissipation coefficient k h , heat sink temperature T hs and t he electric power corresponding to the maximum luminous flux P d. The procedures how to determine the above parame ters are introduced.Then,t he thermal resistances of different types of LED devices are measured.Results show that t he measur ed thermal resistances are highly consistent with the nominal values , which confirm s the feasibility and generality of the propos ed method. This method is simple and credible ,and requires no expensive thermal measuring instruments, making it valuable for engineering application.