Abstract. The characteristic frequency was generated when blasting seismic wave propagate in rock mass. The characteristic frequency played an important role in the amplitude attenuation of seismic wave with time and propagation distance. Rock mass was simplified as visco-elastic media. The time attenuation model of seismic wave amplitude was studied by wave equation and the complex number theory. Theoretical analysis demonstrates that attenuation coefficient of seismic wave amplitude with time is mainly affected by rock viscosity coefficient and elastic modulus. The attenuation coefficient decreases with increase of elastic modulus. The attenuation coefficient increases with increase of viscosity coefficient. The test method of equivalent elastic modulus of rock mass was analyzed according to model of time attenuation of seismic wave amplitude in situ. The wave velocity test verified effectiveness of the method. A new method of determining rock mass mechanical parameter was put forward.