Sulfadimidine (SDD) was detected in pork imported from Mexico by HPLC with gradient elution system. UV spectrum of the peak was measured and confirmed by photodiode array detector, moreover identified by GC/MS after methylation with diazomethane. Content of SDD in the sample was 0.1 ppm and detection limit of SDD by the proposed method was 0.02 ppm. Application of this method to CLP, SMR, SMM, SDM and SQX was studied, and satisfactory results were obtained.