The invention relates to AC-LED thermal resistance and junction temperature testing, in particular to a method and device for measuring the thermal resistance and junction temperature of an AC-LED with alternating current pulses. The device for measuring the thermal resistance and junction temperature of the AC-LED with alternating current pulses is provided with a signal generator, a voltage/current amplifier, an oscilloscope, a temperature control platform, a current/voltage probe, an integrating sphere and a spectrograph, wherein the output end of the signal generator is connected with the input end of the voltage/current amplifier, the output end of the voltage/current amplifier is connected with the AC-LED to be measured, the AC-LED to be measured is fixed to the temperature control platform, the current/voltage probe is connected with the temperature control platform, the signal output end of the current/voltage probe is connected with the oscilloscope, the integrating sphere is connected with the AC-LED to be measured, and the optical power output end of the integrating sphere is connected with the spectrograph. By adopting positive and negative narrow pulses, the junction temperature is hardly influenced; compared with square signals with the same amplitude, the temperature of a thermal sink is adjusted to make the amplitudes of the positive and negative narrow pulses and the square signals equal, and the temperature difference and thermal resistance of the thermal sink and the PN junction are determined.