The　power　transformer　life　cycle　cost　model　is　proposed　based　on　the　interval　analysis,　which　covers　the　investment　cost,　loss　cost,　environment　cost,　operation　and　maintenance　cost,　failure　cost　and　discard　cost,　produced　in　the　life　cycle　of　transformer　and　undertaken　by　the　yearly-equivalence　method.　The　best　economy　case　is　determined　by　comparing　the　yearly　interval　life　cycle　cost.　Different　parameters　of　transformer　life　cycle　costs　are　reasonably　treated　as　the　interval　numbers　and　the　uncertainty　of　each　parameter　is　taken　into　account　in　the　whole　calculation　process.　The　computing　software　IntervalCal,　programmed　with　C++　language,　is　used　to　estimate　the　interval　cost,　and　only　once　is　necessary　to　get　the　transformer　life　cycle　cost　containing　the　uncertain　risk.　The　model　is　applied　in　the　transformer　selection　of　a　500　kV　substation　to　verify　its　effectiveness.　The　interval　life　cycle　costs　of　three　schemes　are　calculated　and　the　best　one　is　determined　by　cost　comparison.