Abstract: In order to study the propagation law of fracture during hydraulic fracturing in coal reservoir, we carried out hydraulic fracturing experiment by using large size triaxial test equipment and specimens made of similar materials. The experimental results indicate that the total propagation direction of hydraulic fracture is the resultant vector of the maximum and the minimum principal stress, which extends along the direction of the maximum force. The existence of natural fractures will affect the expansion path of hydraulic fractures, some of the fractures extend through the weakness or extend to the surface tip of natural fractures, then continue to extend along the direction of maximum principal stress; part of the fractures occur stratification, steering before natural fracture surface.