Abstract: In order to study the environmental characteristics of metamifop for correctly appraising metamifop in the environment for the photodissociation behavior, as well as providing scientific basis for guiding metamifop scientifically and reasonably use. Photolysis of metamifop was determined in organic solvents and aqueous solution under the high pressure mercury lamp and xenon lamp. The results showed that: under the irradiation of mercury lamp and xenon lamp, the photolysis half lives were 2.1 h and 9.3 h. Photolysis of metamifop half-life in organic solvents were 2.5-25.3 h. The photolysis rate of metamifop in different of organic solvents showed following sequences: methanol>ethanol>n-hexane>actone. Metamifop photolysis rates were decreased with the initial concentration increasing. Initial concentration, the type of organic solvent, length of the radiation wave length were related to the photolysis rate of metamifop.