The invention discloses a piriformospora indica microbial inoculum and a preparation method thereof, the piriformospora indica microbial inoculum comprises a fermentation carrier containing piriformospora indica thalli as an active ingredient, a spore protective agent, a dispersing agent and a spreading agent, the content of piriformospora indica chlamydospore in the fermentation carrier is (1.0-20.0) * 10 < 6 > spores/g, the weight percentage of the dispersing agent and the spreading agent is 1-5%, and the weight percentage of the spreading agent is 1-5%. The weight percentage of the spore protective agent is 0.05 to 0.1 percent. The method successfully solves the problem that piriformospora indica is difficult in spore production, large-scale application and long-term storage, when the seed solution is prepared, soluble starch is adopted as a carbon source, compared with other carbon sources, the growth speed of piriformospora indica hyphae can be remarkably increased, the spore production time is remarkably shortened, the spore production quantity is increased, and the production cost is reduced. Through solid culture with sorghum and cane sugar as fermentation carriers, the storability is improved, the prepared microbial inoculum can be preserved for a long time, the spore activity can be kept, and possibility is provided for large-area production and application.