Abstract: As an IR target radiation source, portable IR target simulator is widely used in field to evaluate the performance of defense electro-optical system. Since IR target simulator in field couldnt be calibrated accurately, a new method which uses standard IR extended source blackbody and Fourier spectroradiometer to make calibration is presented. The spectral radiance for IR simulator was measured at a given temperature. Then the integral radiance was calculated in the interested wave band. Finally, based on the radiant area of IR simulator, the radiant intensity was calculated at various given temperatures. Experimental results show that the measured radiance curve is consistent with the theory curve in the interested wave band, and the measurement method is proved.