In recent years, researchers have discovered that NADH and NADPH have important functions in physiological and pathological conditions. In this paper we discussed the synthesis and degradation of NADH and NADPH, focused on the function of NADH, NADPH and NADPH oxidase, and described their functions in various pathological conditions such as inflammation, cardiovascular disease, cancer, neurodegenerative diseases. Nowadays, the functions and metabolism of NADH (NADPH) have evoked international research interest; and the underlying mechanism will be better understood.