Abstract: We describe the mechanics characteristic of the coal rock by adopting B-B failure criteria. Moreover, we study the crack evolution rule of coal rock, the internal flow distribution of coal rock and the equivalent permeability of coal rock under different stress ratios (the ratios of transverse stress to vertical stress were 0.2, 1, 2, 3, 3.5 and 4) using the conversion relationship between B-B standard parameters and M-C standard parameters. The research results showed that the internal cracks of coal-rock with the increase of stress ratio, the fracture appeared a phenomenon of decreasing firstly and then increasing. The internal flow of coal-rock was no obvious change when the stress ratios were 0.2, 1, 2 and 3. However, the internal flow of coal rock appeared obvious change when the stress ratios were 3.5 and 4. The vertical permeability and horizontal permeability of coal rock were decreasing firstly and then increasing, but the change of horizontal permeability had been even more pronounced.