One　watt　white　light　emitting　diodes　(LEDs)　were　made　by　GaN-based　blue　light　chips.　The　chips　were　coated　by　YAG　phosphor　and　transparent　silica　gel.　Current　of　900　mA　as　electrical　stress　was　carried　on　the　LED　samples　and　the　optical　properties　of　the　samples　were　observed　by　measuring　the　main　optical　parameters　during　the　aging　test.　After　4　200　hours　of　aging,　the　luminous　flux　rate　of　LEDs　declined　by　a　factor　between　15%　and　18%.　Changes　in　I-V　curves　indicated　the　increase　in　leakage　current,　which　were　caused　by　the　increase　in　defect　density.　Radiant　flux　of　the　blue　light　drawn　from　the　spectrogram　didn＇t　decrease　while　the　yellow　light　decreased　obviously,　which　implies　the　degradation　of　conversion　efficiency　of　YAG　phosphor.　Reasons　for　the　increase　in　color　temperature　and　keeping　constant　in　color　rendering　index　(CRI)　were　theoretically　analyzed.　The　results　of　the　experiment　will　provide　a　reference　to　the　illumination　applications　of　the　high　power　white　LED.