Objective To explore the impact of Hashimoto’s thyroiditis on pregnancy and the therapeutic doses of levothyroxine requirements after pregnancy. Methods 794 cases with Hashimoto’s thyroiditis were recruited in our hospital for four years, and 34 cases in pregnancy were selected as the study group, the 32 non-pregnant women were served as the control group，the relationship of levothyroxine dose and TSH level were analyzed. The levothyroxine intake and serum thyrotropin (TSH) levels of observed patients were detected before, during, and after pregnancy, each time point last for 9 months, but this detection were last for only three consecutive 9-month in patients of control group. There were two ways of levothyroxine supplementation adopted in this study. Patten No.1 (n =11): no change on levothyroxine dose with no subsequent change in each trimester (t1=t2=t3). Patten No. 2 (n=23), multistep levothyroxine dose throughout pregnancy (t1<t2<t3) to maintain the TSH levels to meet the standards of American Thyroid Association (ATA). Results The value of TSH in Pattern No. 2 showed significant difference as compared with Patten No. 1 (2.8±0.5mU/L and 1.3±0.1mU/L, respectively, P<0.003). According to the supplement baseline of L-T4, Pattern No. 2 showed a more increase above 20% than the Pattern No. 1 at 3 months postpartum (P=0.04). Conclusion More than 50% of hypothyroid women with Hashimoto’s thyroiditis need an increase in levothyroxine requirements in the postpartum because of the different storage of .hypothyroid as well the function of auto-immune injury.