In order to study the dynamic permeability changes of coal reservoirs of different coal ranks during drainage and production,the coal rock triaxial stress—strain (matrix contraction and expansion) test system was used to carriy out physical simulation experiments on the dual effects of effective stress and matrix shrinkage on lignite,gas coal and anthracite.Fixing the axial pressure and confining pressure unchanged,changing the gas balance pressure,simulating the characteristics of the reservoir pressure change during the development process,and testing its dynamic permeability.Using experimental results,the rebound characteristics of dynamic permeability of coals of different ranks during drainage and production are analyzed,and the differences in the improvement effects of dynamic permeability of coals are also analyzed.Research shows that: In the process of reducing the gas balance pressure from 5 MPa to 1 MPa,under the dual effects of effective stress and matrix shrinkage,the normalized permeability of lignite coal sample were 1.00,0.60,0.57,0.57,0.52 in sequence,gas coal sample were 1.00,0.64,0.50,0.54,and 0.55,the anthracite coal sample were 1.00,0.74,0.58,0.50,and 0.56.As the gas equilibrium pressure decreases,the dynamic permeability of the coal samples of middle-rank and high-rank declines first and then rises,and the overall is asymmetrical "V" type change law,but the inflection point is slightly different.The dynamic permeability of low-rank coal sample shows a trend of first decreasing and then basically stable,and the overall is oblique "L".Under the influence of the dual effects of effective stress and matrix shrinkage,the dynamic permeability improving effect of the middle-rank and high- rank coal samples is better than that of low-rank coal sample.