The　reliability　of　power　LEDs　has　strong　dependence　on　successful　package　thermal　management.　In　this　paper,　heating　response　curves　of　LEDs　were　recorded　by　the　temperature　sensitive　parameter　(TSP)　method　and　fast-switching　circuit　techniques.　It　provided　a　novel　method　to　analyze　thermal　resistance　composition　of　power　LED＇s　packaging.　Cover-and-block　method　was　presented　to　provide　a　correction　to　the　apparent　thermal　resistance　of　optical　devices,　and　an　electrical　method　to　obtain　radiant　efficiency　was　also　put　forward.