Few epidemiological studies have investigated the relationship between flavonoids and diabetic nephropathy (DN). Therefore, we explored the association between dietary flavonoid intake and DN among 1949 US adults from the National Health and Nutrition Examination Survey (NHANES) 2007–2008, 2009–2010, and 2017–2018. Weighted logistic regression models demonstrated that the total flavonoid intake in the second (OR: 0.642; 95% CI: 0.456–0.906), third (OR: 0.665; 95% CI: 0.447–0.988), and the highest (OR: 0.551; 95% CI: 0.382–0.796) quantiles (versus the lowest) were associated with the decreased risk of DN. Restricted cubic spline (RCS) analyses showed that the total flavonoid intake had a negative linear association with DN (p-value for non-linearity was 0.003). Weighted quantile sum (WQS) regression analyses revealed that flavan-3-ols, flavones, and anthocyanidins were the main contributors for the combined effects of six flavonoid subclasses. Our findings suggested that higher dietary flavonoid intake was associated with a decreased risk of DN, with the greatest influence coming from flavan-3-ols, flavones, and anthocyanidins.