Gas drainage by borehole is one of the most economical and effective methods for comprehensive utilization and disaster prevention of coal seam gas. To study the evolution mechanism of the main controlling factors in the process of coal seam gas extraction, a multi-field coupling model for gas migration was established and solved using COMSOL Multiphysics software. The results indicate that due to the influence of coal pore and fracture network structure, there is asynchrony between the changes in matrix gas pressure and fracture gas pressure, making it difficult for gas to migrate from the matrix. The fracture system and matrix system jointly control the gas migration ability of the coal body. In the early stage of gas extraction, the gas migration process is mainly controlled by the fracture system. At this time, increasing the permeability of the coal seam can effectively improve the gas extraction efficiency; As the gas extraction progresses, the gas migration process gradually shifts to the control of the matrix system. At this time, simply increasing the permeability of the coal body is difficult to effectively improve the gas extraction efficiency. Measures should be taken to improve the diffusion performance of the coal matrix.