To analyze the iodine nutritional status and related factors of mothers with children under 2 years old, we collected data from the 2016–2017 National Nutrition and Health Surveillance of Children and Lactating Women. A total of 1311 mothers from Hebei, Zhejiang, and Guangxi province were included in the study. Urinary iodine concentration (UIC), thyroid-stimulating hormone (TSH), body mass index (BMI), vitamin A (VA), and vitamin D (VD) were measured. The distributions of UIC and TSH were assessed. Relationships between UIC, TSH and the possible factors were analyzed. The median UIC (MUIC) (P25-P75) of total mothers and mothers in lactation was 142.00 µg/L (99.10-209.40 µg/L) and 139.95 µg/L (96.22-208.03) µg/L, respectively. No differences in UI were found between breastfeeding mothers and non-breastfeeding mothers. The prevalence of mothers with UICs < 50µg/L was 5.03%, and 91.30% of mothers showed TSH normality. UICs and UIC distributions were significantly different among the three provinces, and between rural and urban areas. Obese mothers tended to have higher MUIC and higher prevalence of excessive TSH. Linear correlations between lnUIC and VA/VD were observed with or without adjusting for confounding factors. Higher TSHs were observed in both VD deficiency and insufficiency groups (P < 0.01). However, typical U-shaped relationship between TSH and UIC was not observed in this population. In conclusion, Mothers in our study had no iodine deficiency, but numbers of mothers were still having a UIC of < 100 µg/L or > 300 µg/L. Region, area type, age, BMI, VA, or VD should be taken into consideration in the future iodine evaluation and surveillance.