OBJECTIVE： To establish a method for the decoction of isoflavone content and its acid hydrolysis conversion rate in the flower of Pueraria lobata. METHODS： Using the flowers of Pueraria lobata as raw material， the isoflavone with main component of tectoridin in the flower of P. lobata was prepared with ethanol， ethyl acetate extracted， ethanol recrystallized and purified， and it was converted to tectorigenin with hydrolysis in hydrochloric acid. By screening the solvent and wavelength， UV spectrophotometry was established to determine tectovidin and tectorigenin， and calculate the isoflavone content and acid hydrolysis conversion rate of tectoridin （expressed by the relative percentage of tectorigenin）. It was compared with HPLC detection results， the accuracy of UV method was evaluated. RESULTS： The solvent was 70％ ethanol solution containing 1％ triethylamine， and the isoflavone content was detected at wavelength of 339， 274 nm. The linear range of tectoridin was 8.80-29.33 nmol/mL （r＝0.999 9）. RSDs of precision （n＝6）， stability （n＝5） and reproducibility （n＝6） tests were lower than 1.94％； average recovery was 99.7％ （RSD＝1.77％， n＝9）. There were no statistical significances in the contents of total flavonoids （UV： 17.64-25.55 nmol/mL vs. HPLC： 17.39-24.40 nmol/mL） and the relative percentage of tectorigenin （UV： 57.65％-87.59％ vs. HPLC： 55.62％-91.14％）. CONCLUSIONS： The established method is accurate， reliable， and can be used for the rapid determination of acid hydrolysis conversion rate of tectoridin.