The neuropeptide orexin is widely distributed in the nervous system. Previous studies showed that orexin is involved in the feeding behavior regulation by binding to its receptor 1 (OX1R) and receptor 2 (OX2R) to activate the downstream signaling pathway. Recent studies have demonstrated that the system of orexin and its receptors are also involved in important physiological processes such as sleep-wake, learning and memory, and pathological processes of various neurological diseases. In this review, we summarized the research progress on the function of the orexin and its receptor system in physiological and pathological processes, and revealed the correlation between orexin and nervous system diseases, in order to provide the theoretical guidance for the diagnosis and treatment of the related diseases in the future.