Objective To investigate the clinical efficacy of levothyroxine replacement therapy in children with hypothyroidism.Methods 45 children with hypothyroidism admitted from Apr.2015 to Dec.2016 were selected as observation group,and 45 healthy children in the same period were selected as the control group.Children in the control group received regular diet and were paid attention to nutritional balance.Children in the observation group were given levothyroxine sodium on the basis of dietary guidance.The two groups were treated continuously for 6 months.The levels of thyroid function,insulin-like growth factor,indicators for growth and development and inflammatory factors were measured before and after treatment in both groups.Results After treatment for 3 months and 6 months,the levels of FT3,FT4,IGF-1,IGFBP-3 and IGF-1/IGFBP-3 in the observation group increased significantly compared with those before treatment,and the levels of TSH in the observation group decreased significantly(P＜0.05).The levels of FT3,lFT4,TSH,IGF-1,IGFBP-3 and IGF-1/IGFBP-3 in the observation group after treatment for 6 months were (7.17±0.06)pmol/L,(2.74±0.07)mU/L,(207.67±9.06)μg/L,(0.46±0.02) mg/L and(34.59±1.97).The difference was not statistically significant (P＞0.05).After 3 months and 6 months of treatment,the height,body weight,osteocalcin and 25-(OH)2D3 levels in the observation group were significantly higher than those in the control group (P＜0.05),and there was no significant difference between the two groups after 6 months (P＞0.05).The difference was statistically significant (P＜0.05).Conclusion Left thyroid hormone replacement therapy can significantly improve the thyroid function of children with hypothyroidism,increase the level of thyroid-associated hormone and insulin-like growth factor,promote the growth and development of children,which is worthy of clinical application.