Abstract: Fractures are the main part of karst systems. Fracture flow has a significant influence on the flow in the karst systems. The mechanism of fracture flow needs further researches. Based on the physical models of complex-single fractures with different turning angels and apertures, laboratory experiments are conducted to investigate the relationship between fractures hydraulic head loss and turning angels (varying from 0° to 165°) under different velocities (varying from 0 to 40 cm/s) and different apertures (1 to 2.5 mm). The curves of hydraulic head differences under the conditions with fractures and without fractures are obtained. Based on energy equations, the total hydraulic head losses calculation formula is obtained. Based on the verified Cubic Law and Darcy-Weisbach equation, the local hydraulic head losses are calculated, and the local hydraulic head losses are also obtained. The results show that both the total hydraulic head losses and the local hydraulic head losses increase with the increasing aperture and velocity. Using curve fitting, the relationship between the total hydraulic head loss and velocity is quadratic function and the relationship between the local hydraulic head loss and velocity is found to be expressed as a quadratic function, which can be depicted as the Forchheimer function. The quadratic term coefficients increase with the fracture aperture. In addition, the distributions of the quadratic term coefficients and the first term coefficients are obtained. The quadratic term coefficients occur between the upper envelope curve and the lower envelope curve. The first term coefficients of the total hydraulic head loss varies from -0.1 to 0.5, while the first term coefficients of the local hydraulic head loss varies from -0.1 to 0.25.