Ferroelectric　polymer　films　have　attracted　considerable　academic　and　industrial　interests　due　to　their　dielectric　and　ferroelectric　properties.　However,　the　mechanisms　of　the　dielectric　and　ferroelectric　properties　of　ferroelectric　polymers　are　not　well　understood.　In　the　present　study,　multiscale　characterization　techniques　are　employed　to　analyze　the　microstructure　and　dielectric　properties　of　PVDF　polymer　films.　The　results　obtained　show　that　the　crystallization　behavior　and　related　dielectric　and　ferroelectric　properties　of　PVDF　films　are　affected　by　both　intrinsic　and　extrinsic　effects,　while　the　oriented　amorphous　fraction　layers　play　an　important　role　corresponding　to　the　extrinsic　effect.　For　the　nano-grained　PVDF　films,　the　interfacial　electric　field　ascribing　to　oriented　amorphous　fraction　layers　plays　the　major　role,　and　the　films　have　the　minimal　fraction　ratio　of　polar　phase　and　the　minimal　dielectric　loss.　In　contrast,　the　influence　of　the　ferroelastic　effect　is　larger　than　that　of　the　interfacial　electric　field　when　the　grain　size　is　larger　than　100　nm.　The　micro-grained　PVDF　films　have　the　maximum　fraction　of　polar　crystalline　phase　and　maximal　dielectric　constant　at　grain　sizes　around　5　μm,　whereas,　the　influence　of　the　extrinsic　effect　on　the　crystallization　and　the　motion　of　molecular　chains　of　β-phase　crystalline　could　be　negligible　for　coarse-grained　PVDF　films　with　grain　sizes　being　larger　than　30　μm.　Hence,　the　dielectric　and　ferroelectric　properties　of　ferroelectric　polymer　films　could　be　effectively　functionalized　by　modulating　the　grain　size　and　fraction　ratio　of　the　nonpolar-　and　polar-　crystalline　phases.　©　2024　Acta　Materialia　Inc.