Abstract: The evolution mechanism of slippage effect of coalbed methane reservoir under pore pressure and coalbed methane desorption is explored. Based on the change of pore volume in coal rock, the influence of porosity evolution on slippage effect is discussed. On this basis, a second-order slippage effect model considering dynamic porosity is established. The influence mechanism of different pore pressure and porosity on the slippage effect of coalbed methane reservoir is further quantitatively analyzed. Through theoretical and experimental research, the results show that the pore structure of coalbed methane-bearing coal rock changes with pore pressure and reservoir gas desorption, which in turn changes the porosity, resulting in the dynamic evolution of the slippage coefficient. The slippage coefficient increases first and then decreases with the increase of pore pressure. In the early stage of pore pressure decline, the influence of pore pressure on pore volume is less than that of reservoir gas desorption, which leads to the increase of porosity and the decrease of slippage coefficient. In the later stage of pore pressure decline, the influence of effective stress on pore structure is greater than that of matrix shrinkage effect, which leads to the decrease of porosity and the increase of slippage coefficient, and the rate of permeability increase becomes faster. Under the same pore pressure, the slippage coefficient is inversely proportional to the relative molecular mass of the seepage gas, and increases with the increase of temperature. The prediction results of the model in this paper are in good agreement with the measured data, which can correct the error caused by the overestimation of the slippage effect by the traditional model. It is also more in line with the nonlinear characteristics of the seepage curve with the reciprocal of pressure, which has certain theoretical and practical significance for the development and utilization of coalbed methane.