The aim of this work was to develop an automated on-line solid phase extraction (SPE) with liquid chromatography-tandem mass spectrometry method for the detection of fifteen sulfonamides in pork and fish samples. Samples were extracted with 0.2% formic acid acetonitrile solution, purified by on-line SPE device with HLB column, then separated by XBridge C18 column, using 0.1% formic acid solution and acetonitrile as the mobile phase. Mass spectrometric data was acquired under multiple reaction monitoring (MRM) mode using positive ionization electrospray. Internal standard method was used in the quantification, good linear relationship was got in range of 0.1–100 ng/mL and correlation coefficient was higher than 0.9990. The limits of detection were in the range of 0.125–2.00 g/kg and the limits of quantitation were in the range of 0.250–5.00 g/kg. Recoveries of the method were in range of 78.3%–99.3%, relative standard deviation were lower than 10%. The method was simple, sensitivity, and could be used for routine supervision and analysis of fifteen sulfonamides in pork and fish.