Abstract: The residue of malachite green in aquatic products was determined by the ultra high performance liquid chromatography-mass spectrometry/mass spectrometry(UPLC-MS/MS), and the pretreatment procedure was optimized based on the GB/T 19857-2005 detection method. 100 μL internal standard solution of mass concentration of 100 μg/L was added to 5 g of sample, and mixed well, then 20 mL of acetonitrile, 5 g of acidic alumina were added, and shocked, centrifuged, then 4 mL of the solution was blown dry by nitrogen to 1 mL, and filtered through a 0.22 μm membrane, and then carried out the test. The correlation coefficient r of the standard curve was determined by the standard method:both malachite green, and cryptochrome malachite were 0.999. The recovery rate of malachite green was 71.7%, 95.2% and 89.9% respectively, and the precision was 4.47%, 4.26% and 8.57% respectively. The recovery rates of cryptochrome malachite green were 93.3%, 98.8% and 89.7% respectively, and the precision was 8.73%, 6.87% and 9.71%, respectively. The test results met the requirements of relevant standards and system documents.