To reduce the effects of smoke temperature on the transmittance measurement in 8-14 μm waveband, the transmittances of infrared smoke was analyzed with and without infrared radiation source. Results show that the transmittances of 5 g smoke agent is 40%-50% and 15%-20%. And the infrared smoke formed by burning leads to smoke cloud with a strong radiation. Then, a different correcting method was carried out. The transmittance is corrected by subtracting from the transmittance of infrared smoke without infrared radiation source, and transmittance of the smoke agent with infrared radiation source decrease to 25%-35%.