Metal　coated　dispenser　cathode　is　of　great　interest　due　to　its　low　operation　temperature,　high　current　density　and　long　lifetime,　however,　the　emission　mechanism　is　still　far　from　being　fully　understood.　In　this　work,　the　tungsten　dispenser　cathodes　were　coated　with　iridium　film　of　300　nm　in　thickness.　The　phase　transition　and　surface　structure　evolution　during　cathode　activation　was　systematically　investigated.　The　as-deposited　iridium　coating　shows　a　columnar　grain　morphology　with　ultrafine　size.　Upon　heating　for　1　h　at　1150　degrees　C,　a　multiple-layer　of　Ir/　Ir3W/IrW　was　detected　and　it　fully　converted　to　IrW　layer　after　4　h　heat　treatment.　Such　a　structure　evolution　can　be　well　explained　based　on　thermodynamics.　The　Ir　-＞　Ir3W　-＞　IrW　phase　transition　induces　obvious　film　thickening　and　grain　coarsening.　The　full　activation　could　increase　the　emission　current　density　from　17.35　A/cm(2)　to　30.92　A/cm(2)　at　1050　degrees　C.　Density　function　theory　(DFT)　simulation　results　demonstrate　the　enhanced　emission　of　IrW-coated　cathode　may　be　due　to　its　balanced　adsorption　behaviors　with　Ba　and　O　atoms.　Our　findings　will　provide　deeper　insights　into　the　design　and　development　of　metal　coated　cathodes　with　better　performance.