This study presents a novel approach based on wet chemical oxidation (WCO) for the sequential measurement of stable carbon isotopes in carbonate (delta C-13(Carb)) and organic carbon (delta C-13(OC)) from a single sample using a continuous-flow isotope ratio mass spectrometer (GasBench II-IRMS). The method employs an improved WCO procedure, replacing traditional Na2S2O8 with CrO3-H2SO4 as a strong oxidant, significantly enhancing oxidation efficiency for refractory organic carbon, such as carbon black (GBW4407). This approach addresses the limitations of traditional persulfate-based WCO methods for refractory organic carbon analysis and conventional elemental analyzer-IRMS (EA-IRMS) for trace organic carbon analysis in both bulk solid and aqueous samples. Additionally, a newly designed reaction container was developed to optimize reaction processes, enabling carbonate and organic carbon isotope measurements adopting in-situ reaction on a single sample. Experimental results demonstrate that CrO3-H2SO4 achieves complete oxidation of carbon black, significantly outperforming conventional persulfate-based oxidants (Na2S2O8). Although the CrO3-H2SO4 blank carbon contribution (similar to 0.73 mu g C) was slightly higher than Na2S2O8 (similar to 0.23 mu g C), its nearly uniform carbon isotopic composition (delta C-13(Blank) = -29.54 +/- 0.77 parts per thousand VPDB, n = 19, 1SD) ensures reliable blank correction. delta C-13 values of selected reference materials determined using this method are consistent with accepted values with standard deviation of +/- 0.19 parts per thousand after blank correction. delta C-13(Carb) and delta C-13(OC) measurements were examined on marine sediments and loess/paleosol samples using this new platform. Triplicate measurements yielded precisions of 0.05 parts per thousand and 0.1 parts per thousand for delta C-13(Carb) and delta C-13(OC), respectively. The mean values are in excellent agreement with those obtained from separate measurements using the GasBench II-IRMS and EA-IRMS, confirming the reproducibility and reliability of the new method. This study provides an efficient, simple, and high-precision method for stable carbon isotope analysis, particularly suited for trace and refractory samples. This advancement offers robust technical support for carbon isotope studies in fields such as geology, paleoclimate, and paleoecology.