More　concerns　to　iridium　complexes　are　recently　put　on　light-harvesting　applications　due　to　its　fast　spin-orbital　coupling　and　long　triplet　lifetimes.　The　strategies　and　rules　on　how　to　tune　the　emission　energy　and　improve　emission　efficiency　of　the　iridium　complexes　are　well　established　after　active　investigations　in　the　past　two　decades.　However,　the　knowledge　on　how　to　extend　the　absorption　response　of　the　iridium　complexes　toward　lower　energy　of　the　visible　region,　and　improve　quantum　yields　and　lifetimes　of　the　excited　triplet　state　by　rational　molecular　design　are　still　deficiency　for　scientists.　Meanwhile,　these　parameters　are　crucial　important　for　iridium　complexes　to　be　efficient　photosensitizer.　In　this　review,　the　general　photophysical　process　of　the　iridium　complex,　the　developed　strategies/rules　for　tuning　the　absorption　properties,　triplet　lifetimes　and　quantum　yield　of　the　iridium　complexes　are　discussed.　The　relationships　between　the　molecular　structure　of　the　iridium　complexes　and　their　photophyscial　characteristics　related　to　photosensitization　behavior　are　elucidated.　Also　the　recent　development　of　the　dye-sensitized　solar　cells,　triplet-triplet　annihilation　energy　upconversion,　and　photoinduced　hydrogen　production　using　iridium　complexes　as　photosensitizer　are　reviewed.