Triterpenic acids (TAs) commonly found in the plant kingdom are one of the most important natural ingredients owing to their various pharmacological activities. However, the determination of TAs through a rapid and efficient analysis method still remains a significant challenge because their isomers coexist in many plant samples. Herein we established a quick and sensitive determination approach for five TAs by pre-column derivatization coupled with HPLC-fluorescence detection, using 2-(5H-benzo[a]-carbazol-11(6H)-yl) ethyl hydrazine-carboxylate (BCEHC) as the labeling reagent. In addition, the relationship between the labeling reagent and the separation of TAs was further investigated by using another labeling reagent 2-(12-benzo[b]acridin-5-(12H)-yl)-acetohydrazide (BAAH) as a reference. The results of the method validations showed that both BCEHC and BAAH had good linearity with R² ≥ 0.9907 and R² ≥ 0.9998, exhibiting their own advantages at the same time. For five TA standards, BCEHC had lower limits of detection (0.42–1.35 μg L⁻¹) while BAAH had a shorter retention time. Both labeling reagents can favorably satisfy the requirement of rapid determination of TAs. BCEHC was also applied to detect TAs in Caragana korshinskii Kom. (CK) exhibiting reliable outcomes. It has been verified that there are some TAs in the flowers, leaves and bark of CK. Moreover, asiatic acid and oleanolic acid are the only TAs that exist in every part of it.