A method was developed for the determination of 18 sulfonamide residues in pork by using modified QuEChERS/high performance liquid chromatography with online post column photochemical derivatization and fluorescence detector.The residues in the samples were extracted with 1% acetic acid acetonitrile solution,cleaned by QuEChERS（Quick,Easy,Cheap,Effective,Rugged and Safe) method using a mixture of PSA，C18 and GCB as sorbent.The target compounds were separated by HPLC on a Platisil ODS column（4.6 mm×250 mm,5 μm),and then treated by on-line photochemical derivatization and detected with a fluorescence detector.The optimal conditions were as follows:excitation wavelength:320 nm,emission wavelength:450 nm, column temperature: 36 ℃,mobile phase:0.3% acetic acid-methanol by gradient elution.Under the optimized conditions,a good baseline separation of 18 analytes was obtained.The calibration curves were linear in the range of 0.05-110.28 μg?mL-1 for 18 sulfonamides,with correlation coefficients（r) larger than 0.992 0 .The method detection limits(S/N=3) for target compounds ranged from 1 μg/kg to 18 μg/kg,the limits of quantitation（S/N=10) were in the range of 3-60 μg?kg-1.The spiked recoveries of 18 sulfonamide residues varied from 71.2% to 113.4%,in which the majority recoveries were in the range of 80%-100%.The relative standard deviations(RSDs) were 0.8%-8.7%.The method showed advantages of rapidness,simplicity, less organic solvents,reliability,good accuracy and precision,and could meet the requirements for qualification and quantification analysis of 18 sulfonamide residues in pork.