NOVELTY - Preparation of Bacillus megaterium highly effective petroleum-hydrocarbon-degrading microbial inoculum by using sweet potato starch waste water which is a raw material of a culture medium, comprises (i) preparing a culture medium preparation comprising (a) preparing a strain storing culture medium, (b) activating the strain (liquid 1 l), (c) preparing the seed and (d) fermenting the culture medium (liquid 200 l), (ii) activating the strain, (iii) preparing a liquid seed, (iv) performing liquid state fermentation and (v) preparing the microbial inoculum preparation.    USE - The method is useful for the preparation of Bacillus megaterium highly effective petroleum-hydrocarbon-degrading microbial inoculum.    ADVANTAGE - The petroleum-hydrocarbon-degrading microbial inoculum effectively repairs the soil polluted with petroleum in situ to protect the environment and hence makes use of sweet potato starch waste water with high concentration.    DETAILED DESCRIPTION - Preparation of Bacillus megaterium highly effective petroleum-hydrocarbon-degrading microbial inoculum by using sweet potato starch waste water which is a raw material of a culture medium comprises: (i) preparing a culture medium by (a) adding waste water to a strain storing culture medium (solid 1 l, pH 7-7.5) containing (in g) peptone (2), yeast extract (1), sodium chloride (5) and agar (20), (b) activating the strain (liquid 1l) by adding the waste water up to 1 l (pH 7-7.5) into a mixture of (in g) peptone (2), yeast extract (2) and sodium chloride (5), (c) preparing the seed (liquid 10 l) by adding waste water up to 10 l (pH 7-7.5) into a mixture of soil (1 kg) polluted with petroleum and (d) fermenting the culture medium (liquid 200 l) by adding waste water up to 200 l (pH 7-7.5) into the mixture of the soil (10 kg) polluted with the petroleum, where the above culture medium is sterilized at 115-121 degrees C for 15-30 minutes, (ii) activating the strain by inoculating a petroleum-hydrocarbon-degrading bacteria on the bacterial strains storing culture medium, marking off, separating and purifying, culturing at 30 degrees C until the growth of a single bacterial colony is obtained, inoculating a single bacterial strain into the strain activation culture medium at 30 degrees C and 150-200 revolutions/minute and culturing for 12-36 hours, (iii) preparing a liquid seed by introducing the seed culture medium into a fermentation tank, inoculating the petroleum-hydrocarbon-degrading bacteria with an inoculation volume of 5-10% at 30 degrees C and culturing aerobically for 12-36 hours to obtain the liquid seed, (iv) carrying out liquid state fermentation by introducing the fermentation culture medium into the fermentation tank, introducing the petroleum-hydrocarbon-degrading bacteria seed with the inoculation volume of 5-10% at 30 degrees C, culturing aerobically for 18-60 hours to obtain a culture product with viable bacteria and (v) preparing the microbial inoculum by performing bacterial calculation of the cultured fermentation liquid, mixing with corn straw in a ratio of 1:1, allowing to stand and ventilating until the water content is 30%, packing and storing in a dry place.