The　low-cycle　fatigue　(LCF)　deformation　behavior　of　the　Inconel　718　(IN718)　specimen　with　micro-notch　was　investigated　by　an　in-situ　fatigue　test　inside　a　scanning　electron　microscope　(SEM)　combined　with　electron　backscattered　diffraction　(EBSD).　The　initiation　condition　and　propagation　path　of　cracks　were　observed　by　SEM.　The　essential　reasons　for　crack　initiation,　propagation　and　fatigue　fracture　are　elaborately　characterized　by　crystallographic　information　obtained　from　EBSD.　Meanwhile,　the　strain　evolution　during　fatigue　deformation　simulated　by　the　crystal　plastic　finite　element　(CPFE)　method　is　consistent　with　the　experimental　content,　which　further　verifies　and　supplements　the　experimental　results.　Two　LCF　deformation　mechanisms　(location-related)　of　the　IN718　specimen　are　proposed　at　grain-scale　based　on　the　direct　observation　of　crack　characteristics　and　in-depth　analysis.　Near　the　edge　micro-notch　region,　the　deformation　mechanism　is　mainly　related　to　crack　initiation　and　propagation:　the　plastic　strain　localization　along　the　most　easily　activated　slip　band　leads　to　the　initiation　of　fatigue　microcracks　inside　the　grain.　The　crack　propagation　is　carried　out　by　microcrack　coalescence　in　different　grains.　Away　from　the　edge　micro-notch　region,　the　deformation　mechanism　is　mainly　related　to　the　instantaneous　fatigue　fracture:　fatigue　fracture　comes　from　the　intergranular　plastic　strain　accumulation　and　heterogenous　deformation　at　grain-scale.　The　result　also　deeply　explains　the　fatigue　crack　propagation　in　metals　(two　consecutive　modes).　©　2023　The　Authors