Abstract: In order to explore the mechanism of the engine energy and the surface tension on preparing pesticide emulsions, oil in water, three emulsion in water (EW) formulations, such as 6.9% fenoxaprop-p-ethyl EW, 30% chlorpyrifos EW and 5.7% cyfluthrin EW were carried out. By detecting and comparing the data of the ration of water separation and the particle size distribution of emulsion in pesticide prepared by different apparatus, and the data of the ration of water separation, the particle size and the surface tension of the emulsion in pesticide formulated by different emulsifiers, we found that stable formulations could be formed by using nonionic pluronic(poloxamer) polyester with a broad molecular weight distribution and high molecular weight phosphate esters (acid form) under rotarstator stirrer with high engine energy. As a result, choosing suitable emulsifier to decrease the surface tension and utilizing suitable apparatus to increase the engine energy were favorable in preparing good EW formulation smoothly.