Carbonate δ¹³C data reflecting the primary marine isotope compositions, are crucial for the success of C-isotope chemo. Based on many case studies, two important steps are proposed to evaluate credible isotope data in the study of C-isotope chemo stratigraphy. The first step is to carefully select samples for isotope analysis. The second step is to evaluate the validity of δ¹³C data using elemental geochemical data. Commonly used methods include δ¹³C and δ¹⁸O crossplot, correlation with global secular variation, comparison with C-isotope profiles from other coeval sections,correlatio between δ¹³C and Mn/Sr, and correlation between δ¹³C and Fe/Sr.