Abstract: According to the stress equilibrium equation in pressure relief zone of horizontal direction, combined with Mohr-Coulomb criterion, we deduce computational formula of pressure relief zone width including pore gas pressure. Through relevant parameters of a mine N2105 working face, we carry out theoretical calculation for pressure relief zone width ahead of coal face. Borehole stress sensor is used to measure pressure relief zone width ahead of a mine working face, and the results are basically consistent with the theoretical formula. In pressure relief zone, gas emission quantity increases greatly, and the performance is pressure relief and permeability improvement effect. According to the different borehole failure distance and pressure relief zone width, we give the borehole gas extraction quantity formula for different angles. Combined with field condition of N2105 face, considering borehole forming rate and blind area factor, the reasonable borehole angle is determined.