Objective To understand the urine iodine level of 8-10 year old children at different periods of the day,and explore the feasibility of random urine instead of morning urine. Methods According to cluster stratified sampling method, we chose one urban and one rural primary schools in Hefei. From children aged 8, 9 and 10, We selected 20 people of each age respectively in each school with stratified random sample method, half male and half female. There were totally 120 children,There were 118 children with information completely to be analyzed.We collected the urine samples at 10∶00 am, 12∶30 pm, 21∶30 pm and in the next morning, and detected urine iodine. Results The urinary iodine contents of 118 children in four different periods were 174.4ug/l, 232.1ug/l, 259.7ug/l and 195.0ug/l, respectively. The difference was statistically significant(M＝17.254,P＜0.001). The difference was also statistically significant in urine iodine samples of less than 100 mu g/l, 100 ~299 g/l and 300 g/l and above(M＝12.659,P=0.005). There was no significant difference between 12:30 urine sample and 21:30 urine sample, the next morning urine iodine content and urine iodine frequency distribution(P＞0.05). Urinary iodine in the morning was correlated with urinary iodine levels in other three periods. The correlation coefficient between urinary iodine levels in the middle of 12:30 and the next morning was the highest, and the correlation coefficient was 0.593. The profile analysis showed that the urinary iodine level of children was the lowest at 10:00 am on the same day, then gradually increased, reached the highest at 21:30 am and decreased the next morning. Conclusion It is feasible to monitor urine iodine level with 12:30 urine instead of morning urine.