To systematically observe the effects of seasonal changes on the function of the hypothalamus-pituitary-thyroid (HPT) axis to verify the scientific connotation of the “yin-yang of the four seasons and the five viscera” theory. Methods:The contents of MT, TRH, TSH, T3, T4 in plasma and MT, MR, T3, and T4 in the thyroid tissue of male golden hamster were measured. Results:The results showed that the contents of MT, TRH, TSH, T3, and T4 in plasma showed the highest changes in winter, spring/autumn, and lowest in summer solstice. The contents of MT, MR, T3, and T4 in thyroid tissue showed the highest changes in summer solstice and lowest in autumn and winter. Conclusion:The function of HPT axis has obvious seasonal correlation, and its function is relatively enhanced in winter and spring. Melatonin may be a regulatory factor of this seasonal rhythm. The seasonal function change of HPT axis provides a biological basis for “yin-yang of the four seasons and the five viscera” theory.