Abstract: The growth change of follicular of thyroid gland was detected by using tissue method. Results showed that the follicular of thyroid gland became larger with the increase of days, and the height of follicular epithelial cell at 30 days old was obviously higher than those of the others. The study on the ultrastructure of follicular epithelial cell at 1, 10 and 30 days old showed that the function of epithelial cell was in vigorous stage, while the function of ollicular epithelial cell at 60-90 days old was in relatively stationary state.