Abstract: In order to realize the uniform pressure released, permeability improved and outburst elimination with the hydraulic fracturing in the outburst seam of the underground mine and to reach a miniaturized purpose of the fracturing equipment, a new technique of the porous controlled directional hydraulic fracturing was provided based on the asymmetric pore pressure field. With the theoretical analysis combined with the numerical experiment method, based on the mine geological condition of No.Ⅱ-1 seam in Hebi Mining Area, the RFPA-2D numerical simulation software was applied to study the crack expansion law under the combined influences of the horizontal stress ratio, pore pressure filed as well as the geostress and pore pressure filed. The results showed that the horizontal stress ratio would have remarkable influences to the failure type of the coal, pore shape and pore expansion direction. The distribution features of the pore pressure field could be applied to improve the direction control function of the control borehole and could reduce the hydraulic pressure of the initial fracturing. According to the present geological conditions of the mining area, the horizontal principal stress ratio was ranging from 1.0～1.8 and the controlled water pressure was ranging from 6～12 MPa. Under the asymmetric pore pressure field, when the porous controlled directional fracturing technology was applied, the effect would be best.