Using the thunder signals of a C-G lightning process recorded in the Qinghai region and the theory of signal processing, the frequency spectrum of thunder at observation point is obtained; Based on the propagation theory of acoustic waves, the absorption coefficients in air are calculated and their variations with environmental factors are analyzed. The results show that under a certain profpagation distance and environmental condition, the absorption coefficient increases with frequency increasing. The attenuation of signal below 100Hz is negligible under a certain propagation distance and environmental factors. The attenuations for high-frequency signals of more than 500 Hz are large, their absorption coefficients increase rapidly with the relative humidity inereasing and vary nor-monotonical with temperature. It is deduced that high frequency components of more than 500Hz should be contained in the thunder source.