The high frequency double modulation and lock in technique was attached to the normal Fourier transform infrared spectrometer to eliminate the huge influences of the room temperature background blackbody emission on the measurement of the infrared photoluminescence spectra. The experimental method was optimized by adjusting the modulation frequency, choosing the suitable band pass filter and phase correction. The photoluminescence spectra in 10 μm long wave infrared band without the influences of the background blackbody emission were obtained.