Abstract：In order to study the acoustic wave propagation properties and the ratio of dynamic elastic moduli to static one for unloading rock mass of Three Gorges Project，based on the results of the acoustic wave measurement on the unloading rock mass in the digged slope of the Three Gorges Project，firstly the propagation characteristics of the acoustic wave in rock mass are studied，and the testing results of acoustic wave method are obtained. Taking the ideas and methods of unloading rock mass mechanics，the results of acoustic wave measurement are analyzed and the corresponding changing laws of acoustic wave in different directions and the different wave speed at different altitude of unloading rock slope，which have obvious orthogonal-anisotropy characteristics，are gained. Then different unloading regions are classified based on the propagation characteristics of the acoustic wave，and the macro-mechanical parameters of unloading rocks of each unloading region are determined. Finally the relation between stress and strain in triaxial unloading test is given，and the relation between the relative elasticity modulus Ei and L gained by the finite element analyses is listed. Comparison between the results of the acoustic wave measurement and those of experiment shows good agreement.
