Due　to　thermal　resistance　characteristics　of　fractures,　to　realistically　assess　thermal　effects　of　fractured　rock　mass,　it　should　correctly　reflect　the　thermal　interaction　between　fracture　interfaces.　In　this　study,　the　coupled　FEM-DEM　method　is　extended　to　model　transient　thermal　conduction　in　fractured　rock　mass.　Rock　matrix　and　fractures　are　discretized　into　solid　elements　and　cohesive　elements,　respectively.　To　simulate　thermal　conduction　across　fractures,　the　cohesive　element　is　coupled　with　a　thermal　model　(thermal-cohesive　model)　by　incorporating　an　aperture　dependent　interfacial　thermal　conductivity.　Validation　simulations　indicate　that　the　proposed　model　is　capable　of　capturing　the　temperature　jumps　across　the　fractures　with　different　apertures.　Then,　the　influences　of　fracture　characteristics　on　thermal　conduction　were　numerically　investigated.　Finally,　thermal　conduction　in　highly　fractured　rock　mass　was　studied　by　a　model　with　multiple　randomly　distributed　fractures　generated　through　Monte-Carlo　algorithm.　The　results　indicate　that　the　temperature　gradient　and　heat　flux　field　of　rock　mass　containing　a　single　fracture　are　quite　sensitive　to　fracture　orientation　and　aperture.　Compared　with　the　linear　behavior　between　the　ETC　and　fracture　aperture　in　rock　mass　containing　a　single　fracture,　the　relationship　between　the　ETC　and　fracture　aperture　in　highly　fractured　rock　mass　presents　strong　nonlinear　characteristic.