Abstract: In order to seek the mechanism of the coal and gas outburst, based on the fluid and solid coupling theory, an analysis was conducted on the surface coa lfield drilling, the pressurized test of the gateway in lab and the outburst control effect with the metal fences.A view was provided that the coal gas outburst was the per meability stability lost.The main content of the view would be that the gas pressure gradient of the seam would be a comprehensive index to reflect the mutual influence s between the ground stress, gas pressure and seam permeabilit.A outburst could be divided into two stages.The first stage would be a seam lost stability stage and th e lost stability dynamic occurred would be the gas permeation power.The second stage would be the migration stage of the coal and gas outburst and main power woul d be gas expansion pressure.The gas permeation power would be dependent on the gas pressure gradient and the gas expansion pressure would be dependent on the gas absolute pressure. To reduce the gas pressure in the seam, to increase the air pressure background value in the gateway and to expand the influent access would b e three accesses to reduce the gas pressure gradient.