Abstract: The heat stress reaction and its mechanism of chicken is very complex. As an organism, the chicken agitates all the organ and tissue to deal with the heat stress from environment. The authors discusses the heat stress mechanism of chicken primarily from five aspects of hypothalamus-pituitary - adrenal cortex axis,sympathetic-adrenal medulla system, hypothalamus - pituitary- thyroid axis, hypothalamus - pituitary - sex gland axis, immunity system and summarizes the heat stress reaction of chicken from nutritive metabolism, physiological biochemistry and production.