Abstract: The hydrolysis dynamics of cyhalofop-butyl in aquatic solution was studied.The results showed that the first-order constant (K) was dependent on pH and temperature.The hydrolysis products were identified by HPLC.Cyhalofop-butyl was relatively stable in acid aqueous buffer solutions (pH 5.0),and its stability decreased as pH increased in aqueous buffer solutions.It was readily decomposed in alkaline water.Higher temperature was found to accelerate the hydrolysis.Temperature coefficient of hydrolysis for cyhalofop-butyl was 2.05~3.00.The activation energy of hydrolysis for cyhalofop-butyl was 74.90 kJ/mol.The main hydrolysis products of cyhalofop-butyl were R-(+)-2- propanoic acid,R-(+)-2- -propanoic acid and 2- -propanoic acid.