The emission spectrums of the outer cavity HF/DF chemical lasers were measured.It is found that some spectral lines of HF laser are very week or even disappear unusually.The total atmospheric transmittances of all the spectral lines that have appeared in the spectrums were calculated by MODTRAN software.It is found that those unusual lines of HF laser have poor atmospheric transmission performances.The week intensities or even disappearing of them caused by atmospheric transmission loss in the resonator,which should be counted into the total loss in the resonator.The atmospheric transmission loss has distinct influence on the emission spectrum of HF laser.