NOVELTY - Thermophilic Bacillus (Geobacillus sp.) strain (UTM01) with a preservation number CGMCC No.5641 is new.    USE - The Bacillus strain and microbial inoculum or their fermentation product are useful for preparing composting inoculant for composting sludge (all claimed).    ADVANTAGE - The Bacillus strain UTM01: shows maximum growth rate at 75 degrees C; quickly proliferates in a high temperature composting environment; degrades organic matter; promotes the composting process; and provides the composting inoculant, which has low production cost and stable quality, can be applied in high temperature sludge composting, does not influence the water content of the compost, is environmentally friendly, has good properties and economic benefits.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: (1) microbial inoculum comprising the thermophilic Bacillus strain (UTM01); (2) preparing composting inoculant, comprising (i) activating and culturing the thermophilic strain of Bacillus strain (UTM01) at 60-70 degrees C for 12-48 hours, (ii) inoculating the activated strain into lysogeny broth (LB) culture liquid, sealing a bottle opening, and shaking at 65-70 degrees C for 1-3 days at a speed of 160-200 rotations/minute; (iii) taking the seed liquid (3-10 vol%) obtained in the step (ii), adding sterilized LB culture liquid, controlling the temperature at 65-70 degrees C for every 4-6 hours, ventilating for 10-30 minutes with a ventilation volume ratio of 0.8-1.5:1, stirring for 10-20 minutes for every 12 hours at a stirring speed of 160-180 rotations/minute, and culturing for 2-4 days, and (iv) mixing wheat bran and corn flour in a weight ratio of 1-2:1, respectively adding ammonium sulfate, urea and bacterial liquid, adding saccharides (0.1-0.5%), mixing uniformly until the water content reaches 45-55%, and using 1-2% of lime water to adjust the pH to 7-7.4; (3) composting inoculant prepared by the above mentioned method; and (4) application of the composting inoculant in sludge composting.