A method was developed for determining simultaneously of phoxim, fenthion and coumaphos residues in aquatic products. ［Method］ The samples were extracted with acidic acetonitrile, cleaned up using PSA adsorbent, detected quantitatively by UPLC-MS/MS with external standard method by matrix-match standard solution. ［Result］ At the spiked level of 10~100 μg/kg, the linear correlation coefficient (R) is greater than 0.99, the average recoveries of the 3 organophosphorus pesticides were ranged from 65.8% to 101.0% with 11.4%~16.0% relative standard deviations . The detection limit of these three pesticides was 10 μg/kg and the quantitation limit was 20 μg/kg. ［Conclusion］ The method was simple and reliable, and could meet the requirement of 3 organophosphorus pesticide residue analysis. It could be applied to determine simultaneously phoxim, fenthion and coumaphos in aquatic products.