The morbidity of transient hypothyroxinemia of prematurity (THOP) was high. There is controversial about thyroid hormone supplementation in THOP. Clinical studies suggest that thyroid hormone supplementation can reduce the incidence of patent ductus arteriosus,but no effect on the mortality and the incidence of respiratory disease.Thyroid hormone supplementation can improve the neurodevelopmental outcomes in infants with gestational age less than 28 weeks with THOP, but no effect on infants with gestational age more than 28 weeks. Future research should focus on the normal range of thyroid hormone according to gestational age in preterm infants,and randomized clinical trial welldesigned stratified according to gestational age to study the long-term neurodevelopmental outcome of thyroid hormone replacement therapy in infants with THOP