Abstract: The propagation rules of elastic wave in rock mass with defects take on scale effect, just like the rock mass. The dynamic finite element method (DFEM) is employed to investigate the propagation rules of elastic waves at site-EC37-201-06. The whole computation area is 3.0 ´ 3.2 m² and 15 kinds of computation scales are applied. A static finite element method (FEM) is used to study the relations of elastic wave velocities to the confined pressure and computation scales at site-EC37-101-06. The whole computation area is 1.2 ´ 1.2 m² and 60 kinds of computation scales are applied. The ray theory is used in the former method, and the effective media theory is used in the later. The scale effect of elastic waves is obtained, but there are differences for the two methods. To establish their relations and provide a simple model for engineering computation, a semi-theoretical phase velocity equation is proposed based on the dimensionless method. Compared with the in-situ sonic velocities, seismic velocities and velocities computed by the theoretical model with randomly distributed joints, the proposed equation can be well used in rock mass.