Objective To investigate the incidence of abnormal thyroid function in pregnant women and explore the significance of thyroid function screening in early pregnancy. Methods We randomly selected 630 cases of pregnant women who received routine inspection in the obstetric clinic in our hospital, and gave them five items of thyroid function screening besides routine check at the same time. Then we statistically analyzed the test results, and followed up 61 cases of pregnant women with hypothyroidism or subclinical thyroid function (hypothyroidism) to learn the treatment and adverse pregnancy outcomes,so as tto explore the correlation between hypothyroidism, subclinical hypothyroidism and adverse pregnancy outcomes. Results In 630 cases of pregnant women,there were 8 cases of hyperthyroidism (1.3%),61 cases of hypothyroidism or subclinical hypothyroidism (9.7%),including 5 cases of hypothyroidism (0.8%), 56 cases of subclinical hypothyroidism (8.9%) .There was statistically significant difference in TSH and FT4 between hypothyroidism group and normal control group ( <0.01) .There was statistically significant difference in TSH,FT4 and TT4 between subclinical hypothyroidism group and normal control group ( <0.05) . In 61 cases of hypothyroidism and subclinical hypothyroidism, 39 patients received levothyroxine therapy,22 received no treatment. The incidence of adverse pregnancy outcomes in the treatment group was significantly lower than the untreated group ( <0.05) . Conclusion Thyroid function testing in 6-20 weeks in early pregnancy has important significance in timely founding gestational thyroid dysfunction, so it should be as routine examination project.