〔Abstract〕 Objective To investigate the effects of hypothyroidism and drug intervention on the cognitive function of rat offspring through the establishment of a rat model of experimental hypothyroidism in pregnancy. Methods A total of 20 SD female rats were randomly divided into control group(CON group) and hypothyroid group(PTU group).The hypothyroid model was established by propylthiouracil(PTU), the thyroid hormone levels of female mice were detected by electrochemiluminescence immunoassay, and the differences between the two groups were compared. After successful modeling, the male mice were mated in cages, and the hypothyroid group was randomly divided into no intervention group(group I), first trimester intervention group(group II) and second and third trimester intervention group(group III). The Morris water maze(MWM) experiment was used to test the learning and memory ability of the rats. The morphological structure of hippocampal neurons, the expression of nucleoprotein(NeuN) and synapse-associated protein(SYN) in mature neurons were observed by hematoxylin-eosin staining(HE), Nissl staining and immunohistochemistry. Results (1) Compared with the CON group, the female mice in the PTU group had a significant increase in TSH and a significant decrease in FT4(P<0.05).(2) In the positioning navigation test, the evasion latency of the pups in each group was gradually shortened. On the 5th day, the incubation period of group I was significantly longer than that of groups CON, II, III(P<0.05). There was little change between groups II and III and CON groups(P>0.05).(3) The residence time of group II was significantly different from that in group I during the space exploration stage(P<0.05). There was a significant difference between the number of pups crossing the platform in group I and groups CON, II and III(P<0.05).(4) There was no significant difference between HE staining and Nissl staining in hippocampal tissues of rats in each group. However, compared with the CON group, the average absorbance of NeuN and SYN proteins in the hippocampus of mice in groups I, II and III was significantly reduced(P<0.05). Conclusion Hypothyroidism will have adverse effects on the cognitive function and hippocampal neuron development of pregnant rats, and the effects of intervention on the cognitive function of offspring at different stages of pregnancy are different, the earlier the intervention, the smaller the damage to cognitive function.