Sleep is a life essential process, a biological rhythm. People spend about 1/3 of their lives in sleep. Although people have been observing the natural law of sunrise and sunset for thousands of years, few people have been forced to ask the question of why people sleep until the 12th century, when scientists in the United States began to study sleep, and since then the mystery of sleep, like the Egyptian pyramids, has been the focus of more and more scientists and revealed. Sleep is a complex physiological and behavioral process controlled by the human brain, and sleep and wakefulness alternate periodically. Sleep is relative to wakefulness, when people are relatively awake and have a state of awareness of self and the environment; while sleep lacks the ability to perceive and be aware of external and self-inflicted stimuli. Sleep can be divided into two phases: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep, when the body undergoes a series of physiological changes. During NREM sleep, the heart rate slows down, the respiratory rate decreases, the metabolism of the body decreases, the pituitary gland releases growth hormone and sex hormone, and the muscles, joints and soft tissues of the body relax and get sufficient rest. REM sleep is the result of high evolution of brain, when entering sleep, the body is in sleep state while the brain is in high activity, REM sleep may be the consolidation of instinctive control and regulation of memory traces, playing a major role in the regulation of brain arousal or dream generation. In summary, the important role of sleep on the human body can be the following (1) replenish the body’s sufficient energy: the whole body’s basal metabolic rate decreases during sleep, energy consumption is reduced, while the body’s anabolic metabolism exceeds the catabolic metabolism during sleep, so that the energy consumed by the tissues is replenished, providing energy for eliminating fatigue and physical recovery. (2) Enhance immune function: sleep can enhance the body’s ability to produce antibodies due to a series of endocrine changes, thus improving the body’s ability to resist diseases. (3) Promote human growth and development: As growth hormone is secreted during sleep, it will promote the growth and development of children, and for adults, it can also promote protein synthesis and facilitate tissue repair. (4) Improve intelligence: Sleep can make most of the brain cells in a resting state, so that nerve cells get energy replenishment. At the same time, the rapid eye movement sleep with dreams is good for memory and can prevent the brain from forgetting new knowledge, which helps people’s creative thinking. (5) Benefit life and prolong life: lack of sleep can cause a series of changes in human psychology and physiology, which is not good for health. Adequate sleep can improve health and prolong life. In short, without sleep, the human body systems lose balance, which may lead to death seriously, so it is said that sleep is a physiological need of human beings, without sleep there may not be human beings today.