A high performance liquid chromatography-electrospray ionization triple-quadruple tandem mass spectrometric（HPLC-ESI-MS/MS） method was established for the determination of 18 sulfonamides and their potentiators in veterinary pharmaceutical powder，including sulfadimidine，sulfacetamide，sulfamethizole，sulfachloropyridazine，sulfamethoxazole，sulfathiazole，sulfamonomethoxine，sulfamerazine，sulfadoxine，sulfapyridine，sulfameter，sulfamethoxypyridazine，sulfaphenazolum，sulfadimethoxypyrimidine，sulfisoxazole，sulfaquinoxaline，sulfadiazine and trimethoprim.The 18 banned additives were extracted with methanol-H2O（90∶10）.Then the reconstituted sample solution was analyzed by HPLC-MS/MS under positive ion mode，with a C18 column（2.1 mm×150 mm，5 μm） as analytical column.The detection limits of 18 sulfonamides were all 10 μg/kg.The calibration curves were linear in the range of 50-2 000 μg/kg，with correlation coefficients more than 0.99.The method was validated at spiked levels of 50，200,1 000 μg/kg，and the overall recoveries were in the range of 86.8%-115% with relative standard deviations（RSDs） of 1.0%-9.7%.