In　order　to　solve　the　problem　of　energy　supply　on　the　high　voltage　side　of　the　active　electronic　current　transformer　(ECT),　a　signal　coding　method　based　on　a　three-state　gate　circuit　is　proposed.　The　sampling　clock　signal　and　sampling　data　signal　of　the　analog-to-digital　converter　(ADC)　are　encoded　as　a　four-level　signal　by　the　three-state　gate　circuit,　and　then　directly　drive　the　ultra-high-brightness　LED　to　be　converted　into　optical　signals　and　transmitted　to　the　low-voltage　side　for　decoding.　This　method　requires　only　a　one-way　photoelectric　transmission　system　to　realize　three-wire　SPI　communication,　which　can　reduce　the　power　consumption　of　the　high-voltage　side　to　less　than　5mW,　so　it　can　be　selected　as　a　disposable　high-capacity　battery　power　supply　to　solve　the　problem　of　the　high-voltage　side　of　the　energy　supply.　In　addition,　for　the　problem　of　four-level　signal　distortion　affecting　signal　recognition　and　decoding　found　in　the　experiment,　a　recognition　method　based　on　support　vector　machine　(SVM)　is　proposed.　The　results　show　that　the　recognition　correct　rate　can　reach　99.25%,　and　the　recognition　of　a　single　pulse　takes　only　11.46μs,　which　can　meet　the　signal　recognition　requirements　of　ECT.　©　2023　IEEE.