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This paper introduces occurrence characteristics of coal bed methane in China, and analyses the influence of coal seam permeability on coal mine methane extraction. In addition, it presents the mechanism of increasing permeability by pressure relief. Lastly, the methane extraction technologies are discussed, and the applicable conditions of these technologies are analyzed. It is seen that choosing appropriate methane drainage technology, often in combination with several technologies including ground drilling, underground drilling, and pressure relief and permeability improving measures, is crucial for geological complex coal seam, especially low permeability soft coal seam.

The gas-pulverized coal two phase flow law of gas is simulated by the use of the theory of jet after coal and gas outburst. Research results show that as the volume fraction of pulverized coal in outbursts mixture increases, the speed of two phase flow at the exit gradually reduces, jet core length shorter, turbulent longitudinal effect range smaller, jet width narrower. And dynamic head mainly concentrates in the jet core area and its distribution is more uniform in the roadways. The maximum speed of outburst two-phase flow decreases with the adding volume fraction of pulverized coal, that is higher the coal content in outburst mixtures, smaller the maximum speed after outburst. But a high content of coal have higher impact strike force which can cause major damage effect. The research may provide some theoretical basis for setting underground safety facilities, mine personal protection, disaster warning and emergency rescue.

According to the questions of long eliminating coal and gas outburst period, large projects and slow driving came from the regional measurement of drilling hole ,the paper select 2371 (1) rail transport roadway as experiment for using along seam long drilling as a regional measurement to eliminate coal and gas outburst. Since the regional measurement of along seam long drilling had been carried out, the remaining gas content decreased more than 60％, max Smax was 5.4kg/m, max qmax was 2.01/min.Both Smax and qmax were not beyond the standard. Gas concentrations were not overrun. Gas emission decreased in the roadway afterward. The regional measurement eliminated the risk of coal and gas outburst in effect. Heading face promoted 423m forward safely. The max January footage could reach 120m.Achieve driving of heading face safely and fast.

The experiment studied the variation of coal electric parameter using coal electric parameter testing system designed and processed by themselves. Raw coal sample and moulded coal sample were chosen as the study object. Studies have shown that the resistivity of coal sample decreases with increasing temperature. The resistivity of raw coal decreases significantly as the temperature increases, while the extent of decrease in moulded coal small. The dielectric constant of coal body decreases with increasing temperature. At the same temperature, the dielectric constant and the resistivity of moulded coal are both smaller than that of the raw coal. There are some theory and reference value of the experimental results for predicting coal and gas outburst with electromagnetic radiation.

To improve the low-permeability coal seam gas drainage and gas prevention and to seek the methods to improve the permeability of low-permeability coal, the experimental study on supercritical CO2 on coal was conducted in the laboratory conditions, and the experiment on pseudo-triaxial permeability testing for coal samples, with and without supercritical CO2, was conducted. The results show that due to the effect of supercritical CO2 on coal like physi-chemistry, the porosity of coal was changed, which markedly varied the permeability of coal samples before and after the effect of supercritical CO2; the permeability of the experimented coal samples was significantly higher than before, and average permeability increased by nearly an order of magnitude under the same volume-stress.