A new DEM code corresponding to unconsolidated sand was developed. The flow-coupled DEM simulations for the hydraulic fracturing in unconsolidated sand were performed to reveal the factor that significantly affects the peculiar hydraulic fracturing behavior. Especially, this research focused on the effect viscosity of fracturing fluid. As a result, the two different fracture growth patterns observed in the hydraulic fracturing experiment were successfully represented with different viscosity of fracturing fluid. When the viscosity of the fracturing fluid is 100 mPas or more, the fracture growth pattern of the Linear Fracture was observed. On the other hand, when the viscosity of the fracturing fluid is lower than 100 mPas, the fracture growth pattern became the Branched Fracture. These results indicate that the viscosity of the fracturing fluid have a large influence on the fracture growth process in unconsolidated sand. Moreover, these results suggest that the DEM model may be more appropriate for the analysis of fracturing of unconsolidated materials than the other numerical analysis techniques.