Abstract: Black carbon (BC), a refractory carbonaceous component formed through incomplete combustion of biomass and fossil fuels, plays a critical role in environmental science, climate dynamics, and geochemical cycles due to its stable carbon isotope (δ¹³C) signature. However, traditional analytical methods, such as chemical oxidation and thermal-optical techniques, face challenges including operational complexity, incomplete separation of organic carbon (OC) and BC, and limited analytical precision. To overcome these limitations, this study developed an innovative, fully automated online analysis system integrated with a temperature gradient oxidation furnace, enabling simultaneous separation and isotopic analysis of OC and BC. The system’s core innovation lies in its three-zone temperature gradient oxidation furnace, meticulously optimized to operate at 360, 1 000, 650 °C. These zones facilitate sequential oxidation of OC and BC under controlled oxygen flow. The 360 ℃ zone can ensure complete oxidation of OC while minimizing BC loss, whereas the 1 000 ℃ zone equipped with platinum catalysts can guarantee efficient BC conversion. A final 650 ℃ zone with redox-active materials can remove residual oxygen and impurities. Generated CO₂ was enriched via cryogenic traps, purified through Porapak Q columns, and analyzed using a gas stable isotope ratio mass spectrometer (IRMS) for δ¹³C. Automated sampling and gas-path control modules can enhance reproducibility and reduce human error. OC and BC standard recoveries reach to 88%-95% and 84%-90%, with isotopic standard deviations of 0.25‰ and 0.59‰, respectively. Temperature optimization (360 ℃ for OC oxidation) effectively eliminates cross-interference, achieving residual OC and premature BC oxidation rates below 1%. For real sediment samples, δ¹³C standard deviations of OC and BC remain within 0.31‰ and 0.52‰, underscoring the system’s robustness in complex matrices. A linear response (R²=0.992) in BC quantification was observed across 10-45 μg. Mixed standard tests further confirmed adaptability to varying OC/BC ratios. This system overcomes critical drawbacks of existing techniques by integrating high-precision temperature control, automated workflows, and advanced purification mechanisms. Its ability to perform simultaneous and interference-free OC/BC isotopic analysis significantly enhances data reliability and throughput, thereby offering transformative potential for studies on carbon source apportionment, climate modeling, and biogeochemical cycling. Future adaptations can extend to multi-isotope systems, further advancing precision in environmental geochemistry.