Three commercialized chemicals (Trichlorfon, Masoten and BKC) were studied to determine TLm of eels, and their effects on water quality, phytoplankton, zoo-plankton and residues of water, sludge and fish body. Enzymes were also applied to study the improvement of fish pond water. Results were listed as follows : The 96h-TLm of Trichlorfon and BKC on eels (20.6～25.7cm) were 50 ppm and 4.67 ppm, respectively; After application of Trichlorfonor Masoten, total alkalinity, hardness and conductivity of fish pond water significantly decreased; Use of BKC resulted in algaecide effect and increasing transparency of water; No noticeable effects of enzymes AE and B-500 on water quality were observed.