Abstract：The fractal methods are used to describe the tortuous shape of rock fracture cracks，and the theoretical models for fracture toughness of rock with fractal cracks are built. Based on these and different assumptions，the rock fracture toughness has been determined with rock fracture toughness testing system，which is self-developed and has the internal pressure. The results show that the fracture toughness of rock with fractal cracks is greater than that obtained by linear model，which also confirms that the theoretical values are often lower than the actual pressures of hydraulic fracturing operations at present. It is further proved that the calculation results with this model are closer to the actual ones.
