So as to abstract triterpenoids in betula, we set up spectrophotometric methods to determine the grand totalof the triterpenoids in betula bark. Vanillirr-perchloric acid, glacial acetic acid react with betulin,served as detect sample to determine the grand total of the triterpenoids. The result of experiment showed that the maximum absorption of the system is 551 nm,the temperature of coloring is 70℃, reaction time is 15 min. The linear regression equation is A=9. 198 5C+0. 015 8, r=0. 998 8. Linear range at 1. 0 X 10-2～3. 0～10-2 μg/L. Detection limit is 1. 0 × 10-5μ g/L. The precision RSD is 2. 16%. The rate of recovery is 96. 16%～98. 85%.