Abstract: A microbial inoculant for high-speed humification of organic waste and a preparation method thereof are provided. According to the present disclosure, the microbial inoculant is prepared from Geobacillus stearothermophilus GT1, Thermus tengchongensis GT2, and Thermus amyloliquefaciens GT3. According to the present disclosure, the microbial inoculant prepared from hyperthermophiles with different functions directionally degrades proteins, promotes humification, and degrades complex polysaccharides and organic waste. The resulting products contain rich surface oxygen-containing functional groups, which can adsorb heavy metals and reduce the heavy metal migration rate. Meanwhile, the preparation method of the microbial inoculant provided by the present disclosure can solve the problem that multiple microbial strains are difficult to enrich, and materials for preparing the microbial inoculant can be recycled, which are environmentally friendly and free of secondary pollution.