Objective The aim of this study was to establish a method for determining inorganic， methyl， and ethyl mercury levels in fish using L-cysteine-assisted extraction-high-performance liquid chromatography-inductively coupled plasma mass spectrometry.Methods L-cysteine was used to extract mercury from the samples. The extraction efficiencies of different concentrations of L-cysteine were investigated. The effect of extraction time on extraction efficiency was also studied， and the mobile phase conditions were optimized.Results Using a mobile phase comprising 2% methanol + 0.04 mol/L ammonium acetate + 1 g/L L-cysteine， the three forms of mercury in fish were determined by ultrasonic-assisted extraction with 1% L-cysteine for 10 min. All samples were separated within 9 min. The linear correlation coefficients for the three forms of mercury were over 0.999. The limits of detection of inorganic mercury， methyl mercury， and ethyl mercury were 3.0， 2.0， and 3.0 μg/kg， respectively. The spiked recoveries were 92.2%-97.9%， and the precision was less than 2%. The measured values of the quality control samples were within the range of the fixed values.Conclusion The method developed herein is accurate， simple， convenient， and suitable for determining the three types of mercury in fish.