For detecting the helium density in thermosphere with lidar,we calculated the equivalent width of the aborption spectrum of metastable He 1083 nm emission lines for Gaussia,Lorentzian and Voigtian profiles.Results show that the Voigtian profile contains the information of special broadening mechanics and it is most close to the actual broadened profile.The magnitude of the equivalent width of the He 1083 nm emission lines is about 10-4.Within the temperature range in thermosphere,the equivalent width shows approximate linear relationship with the temperature.The equivalent width increases with the decreasing of the wave length.We have also calculated the 388.9 nm and 318.8 nm emission lines and have gotten similar conclusions.This calculation is helpful in the detection of the helium density in thermosphere.