Abstract: A liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for simultaneous determination of nine diarrhoeal shellfish toxins in shellfish products. In this paper, through optimizing the chromatographic conditions, mass spectrometry conditions, pretreatment methods and other steps, it was finally determined that 80% acetonitrile aqueous solution was used to extract the sample, QuEChERS and dispersed solid-phase extraction technology were used to purify the sample, C₁₈ chromatographic column was used for separation, 5 mmol/L ammonium acetate (plus 0.1% formic acid) buffer and acetonitrile were used as mobile phase for gradient elution, and mass spectrometry was quantified by multiple reaction monitoring mode (MRM) and external standard method. The 9 kinds of diarrhoeal shellfish toxins had a good linear relationship within the mass concentration range of 0.5~50 ng/mL. The linear determination coefficient were above 0.996. The limits of detection were 1~10 μg/kg. The recoveries were 87.2%~111.2%. The relative deviation (n=6) of the measured values was 2.8%~9.2%. The results showed that the method is simple and quick, with high accuracy, sensitivity, reproducibility and cost saving. It was suitable for mass inspection and meets the requirements of practical testing.