The residue and elimination of sulfadimethoxine-sodium were estimated in tissues of channel catfish after a single oral administration at the dose of 200 mg /kg (body weight) at 19 ± 1 ℃, the SDM-Na concentration in tissues was detected by HPLC method.The results showed that the recoveries were in the range of 79%-93%, the detection limit was 0.01 μg /g,the RSD of intra-day and inter-day precision was less then 5%. The plasma concentration-time course of SDM-Na could be described by a twocompartment model,C = 36.68e^-0.14t + 18.12e^-0.05t-54.8e-^0.33t.The main pharmacokinetic parameters were as follows: the distribution half-life of the drug was found to be 4.85 h,peak time was 5.38 h,peak concentration was 21.42 μg / mL.The peak concentration in muscle was 17.93 μg /g at 4 h.The peak concentration in liver was 10.43 μg /g at 8 h,the peak concentration in kidney was 11.61 μg /g at 8 h.The residues were lower than the national standard (100 μg / kg) after 120 h in plasma,muscle,liver,kidney.It suggested that the withdrawal time of SDM-Na should be more then 5 days under this experimental condition.