Abstract: In the paper, an improved formula of atmospheric acoustic scattering cross-section α(θ) is derived and a formula of atmospheric acoustic scattering coefficient αs is established. Moreover, the improved formula of atmospheric acoustic refractive index fluctuation structure coefficient is obtained. The actual measurements show that in the wet air, humidity fluctuation and temperature-humidity cross-correlation fluctuation are the same important factors to atmospheric acoustic scattering attenuation as temperature fluctuation, while in the dry air, humidity fluctuation is ignored.