Abstract: Taking a kind of bulk coal gas emission simulation test device as the main research equipment and the gas diffusion laws as the research object, to understand gas source of mining space at working face of thick coal seam as the main purpose, a simulation study of the gas diffusion laws and gas pressure of thick coal seam about gas emission characteristics is carried out. The results show that the participation of the micro structure significantly changed the gas diffusion laws in thick coal seam, and caused it to show three stage characteristics obviously: the gas emission rate sharply reduced period, like exponential relation and slow reduction period. The laws exhibited in thick coal seam gas emission regularity curves and thick coal seam gas absolute emission did not change obviously with gas pressure change, and the impact of gas pressure mainly reflected in numerical size of gas diffusion velocity; when the gas pressure is fixed, the gas concentration at the working face of the thick coal seam mining is the leading of the coal wall emission from the coal wall. After exposing the new coal wall for some time, the coal wall gas emission is the main reason for the increase of gas concentration in the mining space. Under different conditions of gas pressure, the analysis of the gas source in thick coal seam mining space not only needs to be based on the time of the coal wall exposure, but also needs to be adjusted according to the gas pressure of the working face.