Abstract: The sound velocity in the ethanol water has the typical features,that is,the relationship between the velocity and the concentration appears such trend which is rising first and declining then,obviously it has an extremum.This article makes explanations in a microscopic view,eventually gives the inference that in the low concentration and the high concentration ethanol-aqueous solution emerge respectively two different rigid clusters with chain structure and planar structure under the effect of hydrogen bond.Due to its different stability,they cause different impacts to the bulk modulus,which then lead to the different regularities of the sound velocity in different concentrations.

Key words: ethanol-water binary mixture, acoustical properties, bulk modulus, hydrogen bond, cluster