The biological clock， also known as the circadian rhythm， is a rhythmic activity in living organisms that operates on a cycle of approximately 24 hours. It participates in nearly all major physiological and metabolic processes within the body， playing a crucial role in physiological processes such as sleep， mood， attention， cognition， and learning. An increasing number of studies show that sleep disorders caused by disrupted circadian rhythms can lead to various mood disorders， such as depressive disorder and anxiety. This paper explores the molecular mechanisms related to the changes in circadian rhythm and the occurrence of mood disorders， aiming to provide a theoretical basis for advancing research into the physiological mechanisms of the biological clock and for the prevention and treatment of related mood disorders.