To investigate the associations of composite dietary antioxidant index (CDAI) with risk of cardiovascular disease (CVD) mortality among individuals with type 2 diabetes (T2D). This prospective cohort study included 7551 patients with T2D who participated in the National Health and Nutrition Examination Survey (NHANES) from 1999 through 2018. Death statistics were gathered by connecting the cohort database to the National Death Index through December 31, 2019. Multivariable Cox proportional hazards regression models were utilized to calculate hazard ratios and 95% CIs for the relationship of CDAI with risks of CVD and all-cause mortality. Three multivariable models were built. Restricted cubic spline analyses were utilized to explore the nonlinear association of CDAI with CVD mortality, and nonlinearity was tested by the likelihood ratio test. This cohort study included data from 7551 participants with T2D (mean [SE] age, 61.4 (0.2) years; 3811 male [weighted, 50.5%] and 3740 female [weighted, 49.5%]; median CDAI level, − 2.19 [IQR, − 2.19 ~ − 0.22]). A total of 2227 all-cause deaths and 746 CVD deaths were identified during an average of 98 months of follow-up. Nonlinear associations were observed for CDAI (P<0.05for nonlinearity) with risk of CVD mortality among patients with T2D. Compared with participants in the first quartile of CDAI levels (< − 2.19), the hazard ratios for CVD mortality were 0.47 (95% CI 0.30–0.75) for participants in the highest CDAI level quartile. This cohort study found that higher CDAI levels were significantly associated with lower risk of CVD mortality among individuals with T2D.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13098-023-01109-7.