Objective:To explore the relationship between iodine and hypothyroidism.Methods:Patients with primary hypothyroidism (hypothyroidism group) and healthy people (control group) from Linfen City who first came to the Affiliated Hospital of Shanxi Institute for Endemic Disease Prevention and Treatment in 2017 and 2018 were selected as the research subjects. One random urine sample and fasting venous blood sample were collected from the research subjects. The levels of urinary iodine, blood iodine and serum total triiodothyronine (TT 3), total thyroxine (TT 4), free triiodothyronine (FT 3), free thyroxine (FT 4), thyroid stimulating hormone (TSH), anti-thyroglobulin antibody (TgAb) and anti-thyroid peroxidase antibody (TPOAb) were detected. According to the results of TSH level, hypothyroidism group was divided into hypothyroidism Ⅰ group (TSH≥10.00 mU/L) and hypothyroidism Ⅱ group (4.20 mU/L < TSH < 10.00 mU/L), and they were compared with control group (0.27 mU/L≤TSH≤4.20 mU/L). Results:A total of 97, 96 and 175 research subjects were included in hypothyroidism Ⅰ group, hypothyroidism Ⅱ group and control group, respectively. There was no significant difference in urinary iodine levels among the three groups ( H = 0.631, P > 0.05). The blood iodine levels [(40.70 ± 21.08), (58.59 ± 14.55), (59.50 ± 11.89) μg/L] in the three groups were significantly different ( F = 50.559, P < 0.01), and the blood iodine level in hypothyroidismⅠgroup was lower than that in hypothyroidism Ⅱ group and control group ( P < 0.01). The levels of TT 3 [median (interquartile range): 1.59 (0.99, 2.05), 2.25 (1.98, 2.59), 2.14 (1.89, 2.49) nmol/L], TT 4 [35.18 (16.06, 70.23), 105.68 (83.38, 133.19), 107.18 (89.92, 128.30) nmol/L], FT 3 [3.48 (1.94, 4.52), 5.01 (4.57, 5.50), 5.02 (4.64, 5.55) pmol/L] and FT 4 [7.14 (3.12, 10.76), 15.31 (13.87, 17.11), 16.69 (14.87, 18.20) pmol/L] in the three groups were significantly different ( H = 66.197, 142.461, 94.508, 166.557, P < 0.01). After further pairwise comparison, the levels of TT 3, TT 4, FT 3, and FT 4 in hypothyroidism Ⅰ group were significantly lower than those in hypothyroidism Ⅱ group and control group ( P < 0.01). The levels of TgAb and TPOAb in the three groups were significantly different ( H = 85.507, 101.726, P < 0.01). After further pairwise comparison, the levels of TgAb and TPOAb in hypothyroidismⅠgroup were significantly higher than those in hypothyroidism Ⅱ group and control group ( P < 0.01); and the levels of TgAb and TPOAb in hypothyroidism Ⅱ group were significantly higher than those in control group ( P < 0.01). The correlation analysis showed that urinary iodine was positively correlated with blood iodine ( r = 0.170, P < 0.05); blood iodine was positively correlated with TT 3, TT 4, FT 3, and FT 4 levels ( r s = 0.484, 0.594, 0.383, 0.509, P < 0.01), and it was negatively correlated with TSH level ( r s = - 0.373, P < 0.01). Conclusion:Hypothyroidism patients with TSH≥10.00 mU/L may have low blood iodine level.