Objective To identify the chemical constituents of Xiakucao Xiaoliu mixture by high performance liquid chromatography-high resolution time-of-flight mass spectrometry (HPLC-TOF/MS). Methods The chromatographic separation ACE (3.0mm×150 mm) column was used. The mobile phase was methanol (A) and 0.1% formic acid (B). The gradient elution was: 0-5 min, 5% A; 5-10 min, 5%-15% A; 10-30 min, 15%-45%A; 30-40 min, 45%-70%B; 40-50 min, 70%-90%B. The injection volume was 2 μl. The flow rate was 0.4 ml/min. The column temperature was 25°C. The mass spectrometry was characterized by time-of-flight mass spectrometry, using ESI ion source. The common monitoring was in positive and negative ion mode. The reference ion was m/z 121.9856, 1033.9881. The scanning range was m/z 100-1200. Results A total of 37 chemical constituents were identified in the Xiakucao Xiaoliu mixture, 8 in the positive ion mode fragment voltage of 160 V, 28 in the negative ion mode fragment voltage of 160 V, and 19 in the fragment voltage of 260 V. Both positive and negative ions had 4 responses. The negative ion mode has 16 responses under both fragment voltages. And the ingredients were medicinal. Conclusion An effective method for the identification of the chemical constituents of Prunella vulgaris L. by HPLC-TOF/MS was established, which laid a foundation for its quality control and in-depth study in vivo.