This paper reports the analytic result of the sediment sampled from an experimental area of pen fish-culture in East Taihu Lake. The contents of OM(organic material), TN(total nitrogen) and TP(total phosphorus) in the sediments within the enclosure increase respectively by 48.81%, 13.75% and 22.22% after pen culture for one year, by 70.63%, 47, 62% and 25.00% after two years, by 90.18%, 65.08% and 30, 56% after three years and by 116.86%, 90.48% and 55.56% after four years, as compared with contrast sediments, 20 meters far away from and out of the encircling gear, due to the accumulation of the remains of fish food and seretion. In order to decrease the nutrient load of the sediments in the enclosure net, four points are suggested as follows：1.The type of fish food should be changed. 2.The fish population in the enclosure should be controlled in a proper way. 3.Dead fish should be cleared away from the enclosure in time. 4.The pen culture and plant culture should be carried out alternately.