Changes　in　the　structure　and　composition　resulting　from　oxygen　deficiency　can　strongly　impact　the　physical　and　chemical　properties　of　transition-metal　oxides,　which　may　lead　to　new　functionalities　for　novel　electronic　devices.　Oxygen　vacancies　(V-O)　can　be　readily　formed　to　accommodate　the　lattice　mismatch　during　epitaxial　thin　film　growth.　In　this　paper,　the　effects　of　substrate　strain　and　oxidizing　power　on　the　creation　and　distribution　of　V-O　in　WO3-delta　thin　films　are　investigated　in　detail.　An　O-18(2)　isotope-labeled　time-of-flight　secondary-ion　mass　spectrometry　study　reveals　that　WO3-delta　films　grown　on　SrTiO3　substrates　display　a　significantly　larger　oxygen　vacancy　gradient　along　the　growth　direction　compared　to　those　grown　on　LaAlO3　substrates.　This　result　is　corroborated　by　scanning　transmission　electron　microscopy　imaging,　interface　to　accommodate　interfacial　tensile　strain,　leading　to　the　ordering　phases.　The　strain　is　gradually　released　and　a　tetragonal　phase　with　much　interface.　The　changes　in　the　structure　resulting　from　oxygen　defect　creation　and　optical　properties　of　the　films.　which　reveals　a　large　number　of　defects　close　to　the　of　V-O　and　the　formation　of　semi-aligned　Magneli　better　crystallinity　is　observed　at　the　film/vacuum　are　shown　to　have　a　direct　impact　on　the　electronic　and　optical　properties　of　the　films.