Objective To investigate the distribution of urinary iodine level and its relationship with thyroid function in Tibetan adults in Lhasa. Methods Tibetan residents living in Lhasa and its surrounding countryside were recruited by the method of multistage randomized cluster sampling. Their salt iodine, drinking water iodine, urinary iodine, and thyroid function levels were detected. According to the urinary iodine level, these subjects were divided into the iodine deficiency group ( urinary iodine<100μg/L) , the iodine enough group ( urine iodine 100-199μg/L) , the iodine adequate group ( urine iodine 200-299 μg/L ) and the iodine excessive group ( urine iodine≥300μg/L) . The differences in thyroid function among various groups were compared. Results A total of 2235 subjects were included in the study. The overall level of urinary iodine was in skewed distribution, with a median ( upper and lower quartiles) of 154 (99, 229) μg/L. The proportion of subjects with insufficient iodine intake was 25.7％, while those of the enough, adequate, and excessive groups were 41. 5％, 21. 3％, and 11. 5％, respectively. There was no significant difference in urine iodine level between males and females [152(95,219)μg/L vs 155(100,232)μg/L P>0.05]. The urinary iodine levels in residents of urban were higher than those in rural residents [157(101,232)μg/L vs 140(92,200)μg/L, P<0.05]. The urinary iodine levels in the young, middle-aged, and elderly groups were 175 ( 116,256) , 136 ( 91, 200) , and 116 ( 68, 164)μg/L respectively, showing a gradual decrease in urine iodine level with aging (P<0.05). The average salt iodine content of Tibetan adults in Lhasa was 23.16 mg/kg, and that in drinking water was 4.33μg/L. There were no significant differences in TSH levels among various iodine intake groups ( P>0.05) . The levels of thyroid peroxidase antibody ( TPOAb) and thyroglobulin antibody ( TGAb) were gradually decreased with the increase of urinary iodine level (P<0.05). Conclusion More than 50％ of Tibetans are at the status of low iodine and high iodine intakes in Lhasa. Although the salt iodine content meets national standards, the drinking water iodine content is lower than that standard.