This study presents a hydromechanical model, finite-discrete element method with fluid flow in three dimensions (FDEM-flow3D), that can simulate three-dimensional hydraulic fracturing of jointed rock mass with complex fracture networks. By taking full advantage of a unique topological connection between joint elements and solid elements in three-dimensional combined finite-discrete element method (FEMDEM) together with the cubic law, the authors built a three-dimensional fluid flow model. In addition, a connectivity search algorithm for arbitrarily complex three-dimensional fracture networks is proposed, which can be used to search the connectivity of arbitrarily complex three-dimensional fracture networks. Combining the connectivity search algorithm and the mechanical calculations of three-dimensional FEMDEM, the authors built the three-dimensional hydromechanical coupling model FDEM-flow3D, which directly implements hydromechanical coupling and can simulate fluid-driven fracturing in rock with arbitrarily complex three-dimensional fracture networks. Finally, the authors give five examples to validate FDEM-flow3D in dealing with the problems of steady flow, unsteady flow, hydromechanical coupling, connectivity search of discrete fracture networks, and hydraulic fracturing. The simulation results agree well with the theoretical or experimental results. The model provides a powerful tool for simulation of hydraulic fracturing in shale gas exploitation and geothermal extraction.