In order to get plenty of betulinic acid with high purity and test the content of betulinic acid，betulinic acid was synthesized by oxidizing betulin from the bark of the white birth with Jone’s reagent，followed by selective In order to get plenty of betulinic acid with high purity and test the content of betulinic acid, betulinic acid was synthesized by oxidizing betulin from the bark of the white birth with Jone’s reagent, followed by selective oxidation of the resulting betulonic acid with NaBH4. IR, HPLC-MS,1H-NMR and 13C-NMR were used to identify the structure of betulin and betulinic acid. To compare extraction efficiency, several solvents were evaluated, also extraction time and extraction time were optimized. A quantitative analysis method of betulinic acid by HPLC was formed with ethanol-water (4 g/L ammonium formate) as the mobile phase on Zorbax Eclipse XDB-C8 column (4.6 mm×150 mm, 5 μm)．The flow-rate was 1.0 mL/min and the UV detection was set at 210 nm, with a column of room temperature．The results showed that the optimal extraction conditions were that the white birch bark was extracted 3 h with methanol under reflux at 70 ℃ and the ratio of the bark to the extraction solvent was 15/200(g/mL). The optimal synthesis conditions were that the ratio of betulin to Jone’s reagent was 1∶6 and the mixture was reacted 3 hours at 20 ℃. A good linearity of betulinic acid was in the range of 0.031 25 mg/mL to 0.5 mg/mL (Y=379 381X－2 397,R2=0.998 8). The recovery rate was 97.97%, the RSD (n=9) was 1.64%, and the content of betulinic acid was 96.53%.