Aim To investigate the effect of dietary iron intake on all-cause and cardiovascular mortality in diabetic patients. Methods A total of 5 970 diabetic patients who participated in the national health and nutrition examination survey (NHANES) database of America were included. Baseline data were obtained from the questionnaire and physical examination, and the survival status and cause of death were confirmed according to the national mortality index (until December 1,5). Cox proportional survival analysis was used to estimate the hazard ratio (HR) and 95% confidence interval (CI) for iron intake and all-cause and cardiovascular mortality. Restricted cubic spline analysis was used to explore the existence of nonlinear relationship. Results The mean age of the enrolled subjects was 61.3 years old, 51.3% of whom were male, and their mean dietary iron intake was 14.11 mg per day. During a mean follow-up of 6.3 years, a total of 1 497 deaths occurred. Daily dietary iron intake ＜8.34 mg was set as control group. Compared with control group, the risk of all-cause mortality was the lowest in diabetic patients with dietary iron intake between 11.11 and 14.36 mg (HR 0.83 (0.70～0.99), P＜0.05). Restricted cubic spline regression showed that dietary iron intake was nonlinearly associated with all-cause mortality. However, there was no significant association between dietary iron intake and cardiovascular mortality. Conclusion Dietary iron intake is “L-shaped” associated with the all-cause mortality in diabetic patients, and an appropriate increase of iron intake may decrease the all-cause mortality.