Abstract: OBJECTIVE To make a qualitative analysis on chemical components in water extract of Ligusticum chuanxiong by UPLC-ESI-Q-TOF-MS.METHODS LC-MS/MS， C₁₈(4.6 mm×250 mm，5 μm) column was adopted，with methanol -0.1% formic acid as the mobile phase for gradient elution; ESI ion source was used for mass spectra，and data were collected in positive and negative mode.RESULTS By analyzing positive and negative ion mass spectra information， element composition as well as comparing controls with data from relevant literature， thirteen compounds from water extract of Ligusticum chuanxiong Hort were identified. CONCLUSION After the separation by ultra high performance liquid chromatography， relative molecular mass was determined by mass spectra， and chemical compounds in water extract of Ligusticum chuanxiong Hort were determined by information search through relevant literature data， which served as a powerful proof for pharmacodynamic material basis of water extract from Ligusticum chuanxiong.