Abstract: In order to improve gas extraction in three soft seam, parameter characteristics of different apertures boreholes drilled along seam in Chaohua Coal Mine were measured and studied with the theory of gas flow and rock and soil mechanics.This study shows that gas flow and concentration experienced 3 phases in turn, namely the rapid decline phase, unstable increase and decrease phase and limit phase. In the rapid decline phase, both gas concentration and gas flow in the φ94 mm and φ89 mm boreholes are much more than the φ75 mm boreholes, and the attenuation gradient is significantly less then the other. In the unstable increase and decrease phase, the vibration frequency and amplitude of fluctuation increase by degrees from the biggest borehole to smallest, and the wave period decrease is just opposite. While, there's very little difference from the parameter characteristics in the limit phase. Combined with the construction site conditions, the φ94 mm borehole was selected as the optimal one to extract gas in three soft seams.