The steady broad band radiation signal, from the infrared radiation source, passed through a collimator and propogated atmosphere. It was received by the ABB Bomem MR 170 FTIR spectrometer, the detection system. Based on the spectrometer, a set of surface atmospheric infrared transmittance measurement system in open air was constructed. In Hefei area, the system was used to measure actual atmospheric transmittance. Compared the measured results with MODTRAN outputs, the correlation coefficients are bigger than 0.9, but there are great differences at regions from 2500 cm-1 to 3000 cm-1 and from 4400 cm-1 to 4800 cm-1. By analyzing the changes of water vapor concentration and the transmittance of 2400 cm-1 along with time, the results indicate that the changes of water vapor parameter of local area environment take effect on the transmittance of atmospheric model.