Abstract: In order to research gas emission laws of coal wall in fully mechanized roadway of thick seam, to determine reasonable ventilation design and make gas prevention and control measures perfect, the sub-source prediction method is used to forecast the thick seam fully mechanized roadway. Seleting same place to measure gas emission, the error sources of sub-source prediction is achieved by data analysis and theoretical research. The study show that coal wall perimeter exposed to the roadway section is a function relation with the thickness of coal seam. Finally, the paper puts forward the correction coefficient and formula of gas emission prediction；gas emission law.