The rock mass is a natural damage geological body with both macroscopic and mesoscopic flaws. How to accurately assess the co-effect of these two types of flaws on the rock mass mechanical behavior is an important and difficult issue to be solved urgently. The Elastic-brittle model and Null model in FLAC3D code are adopted to describe the mechanical behavior of the intact rock and these two types of flaws respectively

and the superfine element division method is adopted to divide the numerical model to simulate the rock mass failure. Meanwhile a new method of reflecting mesoscopic flaws by rock porosity is developed to investigate the effects of the void ratio

the pre-crack dip angle and length on mechanical behaviors of the fractured rock mass. The proposed method is adopted to study the effects of these two types of flaws on the factor of safety(FS) and critical failure surface(CFS) of rock slope. The results show that the macroscopic flaws control the failure mode

peak strength and elastic modulus of the rock mass under uniaxial compression

and also govern the failure mode and FS of the rock mass slope. Although the mesoscopic flaws can not change the control effect of the macroscopic ones on the mechanical behavior of the rock mass

they do have some influences on this control effect. In sum

the mesoscopic and macroscopic flaws impact on the rock mass mechanical behavior with different action mechanisms.