Abstract: The paper presented a numerical method to simulate the hydraulic fracture in rock engineering． Based on cohesive elements，a pore pressure cohesive fracture model was developed． To reveal the law of fracture initiation and fracture propagation， the criterion for fracture initiation of quadratic nominal stress and fracture propagation of critical energy release rate was applied． In the numerical analysis，the fracture propagations of fluid with different viscosity and rock modulus were analyzed． The influence of fluid viscosity on the pressure gradient on fracture surface was analyzed，and the fracture patterns in different rock was also studied．