Objective To study the iodine nutritional status in the key population in Tianjin before and after the implementation of the new standards of iodized salt content, and to provide a scientific basis for iodine supplementation. Methods According to the method of population proportion sampling, the family edible salt samples, the urinary iodine and goiter of children aged 8-10 years and the urinary iodine level of pregnant women were investigated before the adjustment of salt iodine content (2005, 2011) and after the adjustment (2014, 2017). The results were compared and analyzed. Results The median of salt iodine after the adjustment (26.05mg/kg) was significantly lower than that of before (30.20mg/kg, Z=12.867, P<0.001). After adjustment, the coverage of iodized salt, the qualified rate of iodized salt, and the qualified iodized salt consumption rate were 78.68%, 81.01%, and 63.74%, respectively, and there were statistically significant differences from before adjustment (92.44%, 96.78%, 89.47%, respectively) (χ²=221.916, 309.405, 540.148, respectively, P <0.001). The median urinary iodine in children aged 8 to 10 years decreased from 210.10μg/L to 172.08μg/L, and the difference was statistically significant before and after adjustment (Z=3.351, P<0.001). The thyroid goiter rate of children decreased from 2.21% to 2.05%, and the difference was not statistically significant between the groups (χ²=0.196, P=0.658). After stratified analysis based on salt iodine content, it was found that among children who took iodized salt and qualified iodized salt, the median urine iodine after adjustment was lower than that before adjustment, and the difference was statistically significant (Z=2.726, 2.742, all P<0.001), but the proportion of urine iodine at an appropriate level was higher than before adjustment. The median urine iodine of pregnant women increased from 145.20μg/L to 147.17μg/L, and there was no significant difference before and after adjustment (Z=1.121, P=0.162). The proportion of pregnant women with median urinary iodine from 150 to 250μg/L was significantly higher in post-adjustment (31.02%) than that of pre-adjustment (24.53%, χ²=4.769, P=0.029). Conclusion After adjusting the salt iodine content in Tianjin, children's iodine nutrition was optimized from a higher level to an appropriate level, and thyroid goiter rate of children remained at low level. The iodine nutrition of pregnant women was slightly lower than adequate level, but the proportion of pregnant women at the adequate level increased. The new standard of iodine salt was appropriate, but the proportion of children with urine iodine <100μg/L increased, which needs to be monitored. At the same time, the iodized salt coverage rate and the qualified iodized salt consumption rate did not reach the elimination standard of iodine deficiency diseases, and the supervision of the salt industry market should be strengthened.