The accurate description of the distribution of hydraulic fracturing fractures is an important prerequisite for the fracturing design and evaluation of fracturing effect. But the position and shape of the fractures have not been described before in the research of description of the branched fracture. So a branches model established on L-system was used and a plane simulation and description method of natural weak surface distribution was established. The natural weak surface was classified using fractal similarity principle，and the corresponding shear strength，tensile strength and the gradient of pressure loss of the fracture fluid after fracturing were known. The simulation method of branched hydraulic fracture distribution was put forward based on the established natural weak surface distribution model and the shear and extension law of fracture. The results show that the number of branched fractures is closely related to the net fracture pressure at shaft wall and difference between the maximum and minimum principal stress. There are multiple branched fractures near the major fractures of hydraulic fracturing and higher net fracture pressure at shaft wall brings more branched fractures. The smaller the difference between the maximum and minimum principal stress is，the more the branched micro fractures open and the larger the connected range is. By using this method，the plane fracture shape and opening condition with fractal characteristics can be simulated. This method also provides the basis for the formation mechanism of complex fracture.