Abstract: During coalbed methane development, the permeability of reservoir is one of the important restricting factors. The paper, adopting lab flowing test of coal cores, has measured the permeability of coal cores under different confining pressure and different flowing pressure, obtained the variation curves of permeability. Furthermore from regression of test data, it was found that there was power exponent relation between the permeability and the ambient pressure in coal cores, and there existed exponential relation between model parameters and injection pressure difference. The analysis of flowing experiment process of 3D permeability indicated that the permeability variation of coal cores is a non-reversible process, the left direction and the right direction of coal cores are more sensible to pressure change. Moreover, in the lower pressure area, permeability change is faster, but in higher pressure area, it is slower. So it should take more attention to the pressure change in the low pressure area during coalbed methane development.