Abstract: The attenuations of sound by molecular absorption (ASMA) in the mean monthly climatic fields of Beijing. Wuhan, Shanghai and Hankou cities are calculated. The results show that ASMA have complicated nonlinear relation with atmospheric temperature and moisture, and they should not be ignored in the detection of turbulent structure coefficient of mixing layer by acoustic radar, but it can be estimated with the surface meteorological data. An approximative method of calculating the attenuations of sound by turbulence is given. When both the attenuations of sound by molecular absorption and turbulence are considered, the magnitude of in unstable conditions obtained from echosonde is more close to the observations from Kaimal et al.