Abstract: Tea gray blight is a severe disease in the tea-planting of China. It can cause leaf dropping easily and even plant death, which impacts the yield and quality of tea greatly. In this study, pathogenic fungus was obtained by isolating and purifying from tea leaves, and was determined through Koch’s rule, morphological and molecular characteristics. Moreover, nano-Mg(OH)₂ was synthesized by co-precipitation, while nano-SiO₂ and nano-TiO₂ were synthesized by sol-gel methods. The size and morphology of nanomaterials were characterized by X-ray powder diffraction(XRD) and scanning electron microscopy (SEM). The mycelia growth rate method was used to determine the inhibition activity of three kinds of nanomaterials at the concentration of 25 mg/mL on tea gray blight. The results showed that the isolated strain clustered in the same branch of Pseudopestalotiopsis theae, and the support rate of self-detection reached 99%, which could determine that the pathogen was P. theae. The morphology of nano-Mg(OH)₂, nano-SiO₂ and nano-TiO₂ were petal-like, spherical and clustered nanoparticles, and the particle sizes in the water were 4 342.72, 1 199.05 and 654.95 nm, respectively, showing certain agglomeration behaviors. The order of activity of the tested nanomaterials was nano-Mg(OH)₂ > nano-SiO₂ > nano-TiO₂, in which the nano-Mg(OH)₂ had the best inhibiting effect, and the inhibiting rate of 150mg/mL nano-Mg(OH)₂ was up to 85.14% at the third day. This study results would provide new strategies and approaches for the effective prevention of tea gray blight.