Objective: To use fast liquid chromatography-triple quadrupole-time of flight mass spectrometry (UFLC-Q-TOF/MS) for analyzing the chemical constituents of flavonoids in traditional Chinese herbal medicine Hedyotis diffusa. Method: The separation was performed on a ACQUITY UPLC BEH C18 Column (2.1 mm×100 mm

1.7 μm) with a mobile phase using 0.1% formic acid ACN (A) and water containing 0.1% formic acid (B)for gradient elution. Time-of-flight mass spect-rometer (TOF/MS) and electrospray ion source (ESI) was applied for qualitative analysis under the negative ion mode.The flow rate was 0.3 mL· min-1

the temperature of column was 40℃. and mass scan range was m/z 100-1 500. Result: Fifteen compounds were identified from flavonoids of H. diffusa. Conclusion: To use UFLC-Q-TOF/MS method can quickly identify the chemical components of H. diffusa which paves a way for further studying the pharmacodynamic material basis of H. diffusa.