Metastable　phase　in　tungsten　film　is　of　great　interests　in　recent　years　due　to　its　giant　spin　Hall　effects,　however,　little　information　has　been　known　on　its　nucleation,　growth　and　phase　transformation.　In　this　paper,　a　900　nm-thick　tungsten　film　with　double-layer　structure　(α-W　underlayer　and　β-W　above　it)　was　produced　on　SiO2/Si　substrate　by　high　vacuum　magnetron　sputtering　at　room　temperature.　The　structural　properties　of　β-W　were　systemically　investigated　by　X-ray　diffraction,　transmission　electron　microscopy,　thermodynamic　calculation,　first-principle　and　phase-field　simulations.　It　is　found　that　the　β-W　nucleation　is　energetically　favoured　on　the　SiO2　surface　compared　to　the　α-W　one.　As　the　film　thickening　proceeds,　β-W[211]　turns　to　be　preferred　direction　of　growth　owing　to　the　elastic　strain　energy　minimization,　which　is　verified　by　phase-field　simulations.　Moreover,　the　β→α　phase　transformation　takes　place　near　the　film-substrate　interface　while　the　rest　of　the　film　keeps　the　β-W　phase,　leading　to　a　double-layer　structure.　This　localized　phase　transition　is　induced　by　lower　Gibbs　free　energy　of　α-W　phase　at　larger　grain　sizes,　which　can　be　confirmed　by　thermodynamic　calculation.　Further　in-situ　heating　TEM　analysis　of　the　as-deposited　film　reveals　that　the　β→α　phase　transformation　is　fulfilled　by　α/β　interface　propagation　rather　than　local　atomic　rearrangements.　Our　findings　offer　valuable　insights　into　the　intrinsic　properties　of　metastable　phase　in　tungsten.　©　2021