Abstract: Hot ethanol-water solution was used to extract the active ingredients from the root of Notopterygium incisum Ting ex H. T. Chang (Notopterygii Rhizoma et Radix), and the microemulsion of the extracted active ingredient was prepared. The physical properties such as stability were tested to evaluate and determine the optimal formulation of the microemulsion. The microemulsion is composed of 15% Notopterygii Rhizoma et Radix extract (notopterol content 0.34%), 9% cyclohexanone, 16% HMK-2100, 10% ethanol, 49.9% water, and 0.1% AF1506. The results showed that the performances of the prepared Notopterygii Rhizoma et Radix extract microemulsion were in line with microemulsion standards. Meanwhile, 5% Notopterygii Rhizoma et Radix extract microemulsion (notopterol 0.11%) and 30% Notopterygii Rhizoma et Radix extract emulsion (notopterol 0.68%) were prepared. The mycelial growth rate method was used to evaluate the effects of different formulations on the four plant pathogens of Rhizoctonia cerealis, Phytophthora capsici, Pyricularia grisea and Rhizoctonia solani. The results showed that 15% Notopterygii Rhizoma et Radix extract microemulsion had significant fungi growth inhibition activities. After 500 times of dilution (Notopterygii Rhizoma et Radix extract 300 mg/L and notopterol 6.75 mg/L), the growth inhibition rates to P. grisea and R. solani were over 90%. Application performance tests showed that Notopterygii Rhizoma et Radix extract microemulsion had excellent spreading and wetting abilities on the leaf of green dill surface.