Abstract: Investigation in 2001 shows that the area of pond crab farming in the Taihu Valley was 11 377.86 hm²,producing 6 681.18 t of freshwater crabs.Calculation based on material balance shows that the total N and total P discharged annually from pond crab farming reached 27.08 kg and 7.85 kg per hm²,respectively,thus amounting to 308.12 t and 89.32 t,respectively discharged to the Taihu Valley in 2001.Analysis of the water drained from the crab ponds shows that total N and total P increased by 0.34 mg·L^-1 and 0.05 mg·L^-1,respectively,in concentration,so the drainage from the ponds would bring 154.74 t of TN and 22.75 t of TP more into the Taihu Lake through the water system every year.