Abstract: In order to reveal the influence of magnitude and direction of ground stress on hydraulic fracture pressure, fracture geometric shape and fracture extension and guide the design and operation of hydraulic fracture to improving gas extraction effect, we simulated and studied the changing behavior of fracture pressure and fracture extension under different ground stress deviations by using software RFPA. The results showed that the hydraulic fracturing process had 3 stages which were prior cracking, initial cracking and cracking and the pressure during cracking was considered the fracture pressure. The fracture pressure decreased linearly with the ground stress deviation increasing. The direction of cracks were determined by the max stress when the ground stress deviation was more than 4 MPa and the directions were complex when the ground stress deviation was less than 2 MPa. With the ground stress deviation increasing, the directions would become single and the extension would become bigger and it was good for gas extraction. The application results were in accordance with the simulated results.