In　optical　current　sensing,　existing　polarimetric　optical　structures　have　relatively　high　measurement　error　and　low　signal-to-noise　ratio　(SNR).　To　resolve　these　challenges,　this　article　proposes　an　improved　composite　polarimetric　structure　with　polarization　offset　(PO)　and　self-calibration　demodulation.　The　proposed　structure　contains　two　single-polarization　optical　paths　(SOPs),　one　of　which　incorporates　PO　to　induce　unidirectional　changes　in　the　polarization　angle.　In　the　SOP　with　PO,　a　waveform　that　matches　the　shape　of　the　current　waveform　can　be　precisely　obtained　by　demodulating　the　sensing　output.　Besides,　in　the　SOP　without　PO,　only　the　effective　value　of　the　current　can　be　precisely　obtained　due　to　bidirectional　changes　in　the　polarization　angle.　Therefore,　the　current　waveform　can　be　calculated　by　self-calibration　between　the　obtained　results.　The　Jones　matrix　derivation　shows　that　the　output　of　the　improved　structure　has　fewer　noise　terms　and　does　not　require　approximation　such　as　existing　structures.　The　test　results　reveal　that　the　small-current　error,　large-current　error,　and　SNR　of　the　proposed　structure　have　been　improved　to　0.8%,　0.2%,　and　37.42　dB,　respectively,　compared　to　1.00%,　0.5%,　and　30.45　dB　of　the　state-of-the-art　structures,　and　high-frequency　fault　currents　are　used　to　demonstrate　the　wide　bandwidth　of　the　proposed　structure.