OBJECTIVE： To prepare reference extract of Sophora japonica and used it as reference substance to determine the contents of 4 flavonoids in S. japonica. METHODS： The reference extract of S. japonica was prepared by water extraction. HPLC method was adopted to determine the contents of rutin， kaempferol-3-O-rutinoside， narcissoside and quercetin. The determination was performed on Diamonsil C18（2） column with mobile phase consisted of methanol-1％ acetic acid （gradient elution）. The detection wavelength was set at 360 nm， the column temperature was 30 ℃， and sample size was 10 μL. The contents of 4 components in S. japonica were determined by using reference extract of S. japonica as reference， and compared with the results with chemical control as reference. RESULTS： In prepared reference extract of S. japonica， the contents of 4 components were 86.85％. The linear range was 0.076 8-3.07 μg for rutin， 0.002 24-0.089 6 μg for kaempferol 3-O-rutinoside， 0.001 59-0.063 7 μg for narcissoside and 0.003 40-0.136 μg for quercetin （all r≥0.999 5）. RSD of precision， stability and reproducibility tests were all ≤2.30％ （n＝6）. The recoveries were 100.4％， 96.99％， 102.3％ and 100.9％（RSD were 2.51％， 1.58％， 2.97％， 3.20％， n＝6）， respectively. There was no statistical significance in the content determination of 4 components between 2 kinds of methods （P＞0.05）. CONCLUSIONS： Using prepared reference extract of S. japonica as reference， established method is simple and reproducible， and can be used for simultaneous determination of 4 components in S. japonica and quality control of S. japonica decoction piece.