The propagation characteristics and evolution mechanisms of hydraulic fractures are of great significance for the efficient development of shale oil resources. In this study, a series of discrete element numerical simulations were conducted, incorporating the characteristics of continental shale reservoirs, to systematically analyze the effects of vertical stress difference, injection rate, and fracturing fluid viscosity on hydraulic fracture propagation. The results demonstrate that the fracture network reaches its highest complexity at a vertical stress difference of 4 MPa. When the injection rate increases from 0.01 m²/s to 0.03 m²/s, the maximum fracture aperture increases by 34.1%, while the breakdown pressure decreases by 7.3%. As the viscosity rises from 0.001 Pa·s to 1 Pa·s, the maximum fracture aperture increases by 25.0%, and the breakdown pressure increases by 20.9%. These findings provide valuable technical insights for the efficient development of unconventional oil and gas reservoirs.