Abstract：Rock mass posses complex structural hierarchy. Such structural hierarchy involves a very wide range of scale levels from atomic scale level to tectonic scale level. This situation makes the concept of elementary volume and Saint-Venant¢s deformation compatibility condition used in continuum mechanics problematic. Internal structural hierarchy influences viscosity and dynamic strength of rock mass，but until now studies haven¢t been seen to link viscosity and dynamic strength of rock mass on different scale levels. This paper，based on the available investigation data and physical mechanical theories，studied the relationship between the viscosity，dynamic strength and the structure hierarchy of rock mass. It is shown from the study that different hierarchy levels correspond to different strength，viscosity and deformation rate. Macroscopic hierarchy scale level corresponds to low strength，low deformation rate and high viscosity，micro-macroscopic scale levels share high strength，high deformation rate and low viscosity. Generally，with the increase of the external loads and the deformation rate，the deformation and fracture consecutively involve macro-，meso-and microscopic levels，correspondingly dynamic strength increases，and viscosity decreases gradually. In moderate and high deformation rate region，dynamic strength increases substantially；viscosity is inversely proportional to deformation rate. Hence strength and viscosity are not constants for one material，but have different values on different hierarchy levels. As for the size of fractured rock，it is related with the dynamic strength which rock mass can reach. Based on the analysis of mechanical behavior of rock mass on different hierarchy levels，approximation formulae for the dynamic strength and viscosity in dependence on hierarchy levels and deformation rate，formula for the determination of fractured rock mass are suggested.
