Abstract: In order to study the effect of the increase of effective stress on the anisotropy of permeability and porosity of CBM formation during the development process of CBM reservoir, coal samples from different directions are adopted and the anisotropy of the CBM reservoir in southern Qinshui Basin is evaluated and the influence of the increase of effective stress on the anisotropy of porosity, permeability and stress sensitivity for CBM reservoir is studied on focus. The results show that the porosity and pore structure of CBM reservoir have obvious anisotropy. The T2 spectrum from NMR in the direction of face cleat is bimodal, mainly developing macropores and cleats, while the T2 spectrum in butt cleat direction is single peak with wide bottom, mainly developing mesopores, with the single peak in vertical coal bedding direction and developing micropores. The NMR signal strength in all three directions decreased, after the effective stress was loaded to 10 MPa, indicating that some pores of these coal samples were compressed and some cleats was closed. The permeability of CBM reservoir has obvious anisotropic characteristics and the permeability in the direction of face cleat is more than 9 times that in the direction of vertical coal bedding. With the increase of effective stress, the degree of anisotropy of reservoir decreases, but the heterogeneity degree of permeability between the face -cleat direction and the vertical-coal-bedding direction is the strongest. The stress sensitivity of CBM reservoir has obvious anisotropic characteristics: the stress sensitivity in the direction of face cleat is the strongest, and the values of the stress sensitivity coefficient and permeability damage rate are the largest. While the stress sensitivity in vertical-coal-bedding direction is the weakest, with the lowest values of the stress sensitivity coefficient and permeability damage rate. After the effective stress unloading, the permeability recovery rate in different directions is different, and the face cleat direction is the highest, up to 55.3%, and the recovery rate of the vertical-coal-bedding direction is the lowest, only reaching to 40.2%.