【Objective】In this paper， by simulating the pond water ecosystem， degradation rule in water and sediment and the impact on aquatic ecosystem of arsanilic acid were studied.【Method】Four mini-aquatic pond ecosystems were established； the control was added 100 g pig manure and treated with different mass concentrations of 50， 150 and 500 mg/L of arsanilic acid. Samples of water and 2 cm-depth-sediment were taken. Arsanilic acid was determined by HPLC and the total arsenic contents were determined by HG-AFS.【Result and conclusion】The half-life of arsanilic acid increased with the extension of the delivery drug concentration in pond water and surface sediment， which was 3.73 to 16.04 d and 35.17 to 61.27 d， respectively， and the total arsenic showed a distinguished subsidence trend in sediment and degraded slowly. The values of dissolved oxygen（DO）， pH， primary productivity（P/R）， activities of sediment alkaline phosphatase and catalase， and the content of total nitrogen and phosphorus indicators were regularly detected. The results showed that 500， and 150 mg/L arsanilic acid could cause irreversibly detectable effects on the ponds. High mass concentration of arsanilic acid obviously inhibited catalase activities. The total nitrogen content of sediment showed an inhibition-promotion-change process， and all mass concentrations of the total phosphorus content declined and presented a concentration dependent relationship.