The kinetic characteristic of photolysis of cypermethrin (CPM) sensitized by acetophenone (AP) and the effect of probe substance 2,6 Di tert butyl 4 methylphenol and tetralin is studied in this report. It showed that the photolysis rate of CPM increases slightly with the increase of AP concentration; photolysis rate of CPM has no relationship with itself; The more dipolar moment the solvent has, the more the interaction between radical and solvent has, and the slower the photolysis of CPM is. The addition of radical probe substance confirms that ROO·is more than RO·. The steady state concentration of ROO· is about 10 -8 mol·L -1 . The kinetic characteristic of photolysis of cypermethrin (CPM) sensitized by acetophenone (AP) and the effect of probe substance 2,6 Di tert butyl 4 methylphenol and tetralin is studied in this report. It showed that the photolysis rate of CPM increases slightly with the increase of AP concentration; photolysis rate of CPM has no relationship with itself; The more dipolar moment the solvent has, the more dipolar moment the solvent has, the more the interaction between radical and solvent has, and the slower the photolysis of CPM is. ROO · is more than RO ·. The steady state concentration of ROO · is about 10 -8 mol·L -1.