Based on high gas density in 1401 working face of Yanjing One Mine, gas emission law in K14 coal seam was studied combining with design of wear layers, consequent layer and goaf drainage system on the basis of surrounding rock geological conditions. According to the relation between field extraction capacity of gas and roof pressure, it was clear that gas emission quantity was closely connected with periodic roof pressure. And roof pressure directly influenced the permeability of coal seam thus affected gas emission.