Abstract: Cancer threatens human's life and its incidence is increasing year by year. The pathogenesis of cancer is complex, and its occurrence is the result of multi-factor interaction and multistage process. With the functions of anti-oxidation and removing active nitrogen oxides, tetrahydrobiopterin(BH4)is a coenzyme of aromatic amino acid hydroxylase and nitric oxide synthase, and plays a key role in a series of physiological and pathological process in vivo. Recent studies has shown that BH4 plays a role in the occurrence and development of malignant tumor, and has double functions in promoting and inhibiting the development of tumor.