LED　has　promised　to　replace　conventional　light　sources　with　impressive　economic　and　environmental　saving　because　of　the　realization　of　high　efficiency　and　long　life　time　light　sources.　Reliability　issue　is　a　key　factor　affecting　the　lighting　quality　and　life　time　of　LED　lighting　system.　Each　LED　system　includes　two　major　aspects;　optical　and　electrical　driver.　The　LED　driver　is　one　of　the　weakest　components　in　the　LED　luminaries　and　they　tend　to　degrade　rapidly　with　increasing　temperature.　The　effect　of　temperature　on　performance　and　reliability　of　LED　driver　is　analyzed　in　this　paper.　A　thermal　simulation　model　based　on　a　tapped-inductor　quasi-resonant　Buck　LED　driver　was　set　up.　The　thermal　field　and　thermal　stress　analysis　of　the　driver　was　done　by　using　the　software　EFD　Pro　8.2.　The　losses　from　various　components　of　the　driver　were　calculated　in　detail.　The　histogram　of　losses　in　various　components　in　the　driver　was　given.　Computer　simulation　and　a　prototype　rated　at　5W,　with　an　input　ac　voltage　of　176-265Vrms　and　an　output　current　of　700mA　has　been　implemented　to　verify　the　prediction.