Abstract: The bioacrumulation and disappearance of ³⁵S-dimehypo in simulated aquatic ecosystem were investigated, using simulated ecosystem experimental facilities and radioisotope tracer techniques. After the experiment for 20 days ,high absorption by Wolffia arrhiza Wimm was found in the ecosystem of water,Wolffia arrhiza Wimm,Ctenopharyngodon indellus and snail. The bioaccumulation ratios of Wolffia arrhiza Wimm was 24. 65% , which is much higher than that of snail or fish. The bioaccumulation ratios of fish parts differed, viscera with the remain of Wolff ia arrhizaWimm (4. 01 %)>. gill (1. 66%)>bone (0. 95%)>meat (0. 52%). After the fish were transferred from the contaminated water to clean water, the disappearance of ³⁵ S-dimehypo in the processes of fish excretion and metabolism was also examined. As a result, the residual pesticide disappears with time, with its half life about 10 days.