Abstract: Water jet depressurization increasing permeability technology is uesed to strengthen the gas drainage in low permeability soft coal seam, the key characteristics such as the average gas emission, coal output and jet orifice are analyzed, the average gas emission rate and coal output are proved as good investigation indexes for water jet depressurization increasing permeability effect. For soft coal seam, the time absolute slope value and gas emission after the last jet orifice are also important investigation indexes, which could show directly the depressurization increasing permeability effect of water jet. Water jet depressurization increasing permeability technology has well effect under the situation of the radial orifice diameter in 4.00 mm and the consistent coefficient of the coal as 0.2.