The　advantages　of　using　supercritical　carbon　dioxide　as　working　fluid　in　geothermal　development　(potential　carbon　dioxide　geological　storage　and　relatively　high　mobility)　have　attracted　considerable　interest　in　the　simulation　of　a　carbon　dioxide-based　enhanced　geothermal　system.　This　study　proposed　a　numerical　model　based　on　the　three-dimensional　unified　pipe-network　method　to　simulate　the　two-phase　flow　and　thermal-hydraulic　coupled　process　in　a　carbon　dioxide-based　enhanced　geothermal　system　considering　complex　fracture　networks.　The　van　Genuchten　capillary　model　and　relative　permeability　model　are　adopted　to　characterize　the　displacement　process　in　both　the　fractures　and　the　rock　matrix.　A　pipe　equivalent　technique　is　employed　to　discretize　the　governing　equations　for　the　two-phase　flow　and　the　heat　transmission　with　the　local　thermal　non-equilibrium　concept.　Two-phase　fluid　transfer　at　material　interfaces　is　solved　based　on　a　pipe　superposition　principle　in　a　pipe-network　system.　Discretized　forms　are　solved　by　a　sequential　implicit　time　scheme　alleviating　the　Courant-Friedrichs-Lewy　condition　in　fracture　networks.　The　proposed　model　is　verified　against　analytical　results　for　the　Buckley-Leverett　problem.　Saturation　evolution　curves　at　different　time　steps　converge　to　the　analytical　solutions　as　the　node　number　increases.　Sensitivity　analyses　using　a　doublet　system　horizontally　embedded　with　one　large　fracture　indicate　that　the　capillary　contrast　between　the　rock　matrix　and　the　fractures　and　the　injection　flow　rate　pose　impacts　on　the　produced　carbon　dioxide　saturation　and　the　outlet　fluid　temperature　drawdown.　The　simulation　of　circulating　processes　considering　randomly　generated　fracture　networks　demonstrates　that　the　more　promising　potential　of　heat　extraction　can　be　achieved　using　the　pure　carbon　dioxide　as　the　working　fluid　instead　of　cooled　water.　Analyzing　the　effects　of　the　initial　reservoir　carbon　dioxide　saturation　shows　that　increasing　the　reservoir　carbon　dioxide　saturation　before　heat　excavation　can　improve　the　heat　production.　Both　increase　the　matrix　permeability　and　the　fracture　aperture　enhances　the　performance　of　the　heat　extraction　and　the　carbon　dioxide　sequestration.