Abstract: To excavate the biological function of Umbelopsis dimorpha, the dominant endophytic fungus in the roots of Vaccinium dunalianum, it was inoculated into the host tissue culture seedlings for drought stress test. It showed that U. dimorpha contributed to the enhancement of peroxidase activity during the normal growth of the plant under normal water conditions. Moreover, the dominant endophytic fungi could rapidly and significantly enhance the peroxidase activity in plantlets under drought stress. This was conducive to the rapid regulation of catalase activity in plantlets. At the same time, the content of proline in plantlets was increased more rapidly and significantly, and the response speed of the regulation of soluble sugar content in plantlets was improved to contribute its accumulation under drought stress. The results indicated that U. dimorpha, the dominant endophytic fungus in the roots of V. dunalianum could enhance the drought resistance of the host.