Due　to　the　significant　scale　and　complex　operating　conditions　of　drive　shafts,　experimental　analysis　of　small　crack　evolution　becomes　challenging.　This　study　presents　a　cross-scale　modeling　approach　to　analyze　the　evolution　of　small　cracks　in　drive　shafts.　Firstly,　by　employing　the　sub-model　method　and　the　variable-node　finite　element　method,　two　mesoscale　models　based　on　crystal　plasticity　theory　are　integrated　into　a　macroscale　model,　constructing　a　cross-scale　analysis　model　for　small　crack　evolution.　Then,　by　measuring　the　heterogeneous　deformation　degree　in　the　mesoscale　models,　models　for　surface　small　crack　initiation　and　propagation,　accounting　for　heterogeneous　deformation,　are　developed.　Besides,　energy-based　models　for　internal　small　crack　nucleation　and　propagation　are　established.　To　simulate　the　initiation　and　propagation　of　surface　small　cracks,　the　study　utilizes　a　mesoscale　variable-node　shell　model　incorporating　the　Crystal　Plasticity　Finite　Element　Method　(CPFEM),　coupled　with　the　Crystal　Plastic　Coupling　Extended　Finite　Element　Method　(CP-XFEM).　From　the　simulation　results,　a　cross-section　of　the　mesoscale　solid　model　is　extracted　to　establish　a　polycrystalline　plasticity　mesoscale　cross-section　model.　Then,　utilizing　the　element　deletion　method　in　ABAQUS,　simulations　for　internal　small　crack　nucleation　and　propagation　are　performed.　The　findings　demonstrate　that　the　cross-scale　model　effectively　reflects　the　irregular　propagation　rate　of　microscopic　small　cracks.　The　propagation　patterns　of　surface　small　cracks　are　generally　consistent,　with　more　significant　path　deviations　observed　in　models　exhibiting　significant　grain　orientation　differences.　In　the　latter　stages　of　internal　small　crack　propagation,　as　the　number　of　failed　grains　rises,　stress　concentration　in　the　microstructure　intensifies,　resulting　in　a　significant　acceleration　phase　in　crack　propagation　and　a　significant　decrease　in　propagation　life.　©　2024　Elsevier　Ltd