Abstract: The cloud point is one of the technical requirements for stable quality of the pesticide microemulsion. The relativity between its components and the cloud point of three kinds of pesticide microemulsion were studied by 17O-NMR. It was shown that cloud point was increased with the strength of hydrogen bonds formed by the surfactants, co-surfactants and water increasing. It was found that the cloud point was decreased with the water hardness increasing. It is necessary to choose more hydrophilicity surfactants and more polarity co-surfactants for increasing cloud point of microemulsion. In order to save the cost and be convenient for plant production, the tap water should be the better choice for the pesticide plant in microemulsion manufacture, and the other measures may be taken to enhance the cloud point of microemulsion.