Abstract: The optimum formulation of 10% chlorfenapyr emulsion in water (EW) was developed by the phase transfer method through the screening of the solvent and surfactant.The optimum solvent was 22.8% toluene.The proportion of the mixture of surfactant,EL-40,Span-80 and 500#,was 16∶ 3∶ 1(m/m),which totally occupied 10% weight of the formulation.The other component was distilled water,which was 56.7% of the formulation.Made by the above formulation,the indexes of the chlorfenapyr EW was up to grade.The formulation had been stored at normal temperature,or (54±2)℃ for 80 days without oil- and layer-separation.The viscosity of the formulation was low,which makes it easier to pour out and sub-package.