Birch(Betula platyphylla Suk.) bark contains important pentacyclic triterpenes as betulin and betulinic acid, which play important functions in anti-tumor and anti-HIV.Cytochrome P450 monooxygenase(CYP450) is essential for the diversification and functional modification of the triterpene skeleton.In this study, five new CYP450 genes were cloned from birch with ORF lengths of 1284bp, 1533bp, 1188bp, 1704bp, and 1539bp, respectively.Phylogenetic tree analysis shown that five BpCYP450 genes are located in five subfamilies, named CYP94B89, CYP89S1, CYP97B62, CYP86B54, and CYP86A182.The expression characteristics of five CYP450 genes in different tissues and their responses to different stresses(MeJA, SA, GA₃, ABA, ethylene, and mechanical damage) were significantly different, among which CYP89S1, CYP97B62 and squalene epoxidase(BpSE) and dammarenediol synthase(BpDS) were highly expressed in leaves.CYP89S1, CYP97B62, and CYP86A182 genes are induced by MeJA and significant synergistic expression effects with lupeol synthase(BpW).CYP89S1, CYP97B62, CYP86A182 have C-28 oxidation function and catalyzing the conversion of lupeol to betulinic acid.Among them, CYP97B62 gene has the highest catalytic efficiency, increasing the content of betulinic acid by 1136%.In addition, co expression of BpMYB21 and CYP86A182 can significantly enhance the conversion and synthesis efficiency of betulinic acid in tobacco(Nicotiana tabacum L.), and CYP89S1 can enhance salt and alkali resistance in yeast(Saccharomyces cerevisiae)