Objective: To develop a method for the simultaneous detection of four sulfonamide residues in prawns—sulfadiazine, sulfathiazole, sulfamerazine, and sulfamethazine—using ultrasound-assisted matrix solid-phase dispersion extraction combined with pre-column derivatization and high-performance liquid chromatography (HPLC). Methods: By optimizing extraction conditions, ethyl acetate was chosen as the extraction solvent and florisil as the solid dispersion agent. Sulfonamides were extracted from prawns using ultrasound-assisted matrix solid-phase dispersion, then derivatized with fluorescamine and analyzed by HPLC with fluorescence detection. Results: The sulfonamides exhibited excellent linearity within the concentration range of 2–100 μg/L, with correlation coefficients greater than 0.999. Detection limits were 0.5 μg/kg and quantification limits were 2 μg/kg. Spike recoveries for blank prawn samples ranged from 84.4% to 93.9% at 2 and 20 μg/kg, with relative standard deviations (n = 3) below 7.7%. Conclusion: The method is straightforward, efficient, and highly precise, meeting the standards for residue analysis.