NOVELTY - The method comprises collecting agricultural and industrial organic waste vinegar residue, cassava slag and mushroom scraps as main raw material, crushing the raw materials, adding vermiculite, perlite and carbide or plant ash, compound fertilizer, synergistic agent and short strong agent as auxiliary material, and preparing prescription A including the main ingredient comprising 3 parts by weight (pbw) of agaricus bisporus scraps and the auxiliary material comprising 0.4 pbw of carbide or plant ash, 0.2 pbw of perlite, 0.4 pbw of vermiculite and 0.1-0.5 pbw of compound fertilizer.    USE - The method is useful for preparing rice seedling organic composite soil.    ADVANTAGE - The method provides easy preparation of rice seedling organic composite soil with high quality.    DETAILED DESCRIPTION - The method comprises collecting agricultural and industrial organic waste vinegar residue, cassava slag and mushroom scraps as main raw material, crushing the raw materials, adding vermiculite, perlite and carbide or plant ash, compound fertilizer, synergistic agent and short strong agent as auxiliary material, preparing prescription A including the main ingredient comprising 3 parts by weight (pbw) of agaricus bisporus scraps and the auxiliary material comprising 0.4 pbw of carbide or plant ash, 0.2 pbw of perlite, 0.4 pbw of vermiculite and 0.1-0.5 pbw of compound fertilizer, moderate synergistic agent and short strong agent, preparing prescription B including the main ingredient comprising 5-6 pbw of vinegar residue and 3 pbw of cassava slag and the auxiliary material comprising 0.4-1.2 pbw of carbonization wrap or plant ash, 0.2 pbw of perlite, 0.4-0.6 pbw of vermiculite and 0.1-0.5 pbw of compound fertilizer and moderate synergistic agent and short strong agent, adjusting the physical and chemical indexes of the material, pretreating the raw material, adjusting pH, carbon-to-nitrogen ratio (C/N) and electrical conductivity (EC) of the organic material using moisture indicator, feeding organic material in the material agaricus bisporus scraps, mushroom scraps, vinegar residue and cassava slag in fermenting vats stacking fermentation tank, where the pile-up depth is 1-1.5 m, or directly preparing the stack of which the width is 1-3 m, height is 0./8-1.2 m and the length is 5-50 m on the cement ground, and fermenting the mixture for 30-60 days, inoculating high-temperature corrodent, feeding the organic material in a fermentation tank or a cement field to stack for 2-3 days, adding high temperature corrodent to stack the organic material, fully mixing the fermenting agent and the material, covering the shielding rainproof material on the fermenting tank and the cement field without a shed, measuring temperature, adding the fermentation strain, measuring temperature twice each day at 9-10:30, stacking 3-5 points of each fermenting tank, where the measuring temperature depth is 35-40 cm and measuring temperature before turning, turning and supplying oxygen, turning the first time when adding the fermenting strain, adopting the principle as to the turning frequency, fermenting within a week, turning once at an interval of two ways even if the temperature does not ascend or increases slowly, avoiding to form an anaerobic environment, ascending the temperature stably after a week, stacking once at an interval of a day, stacking immediately once the temperature exceeds 55 degrees centigrade, increasing the stacking frequency when the temperature is 68-70 degrees C or the material is compact, turning the mixture for 1-3 days, discharging the mixture when the organic material becomes brown and the temperature does not ascend again, discharging after the fermenting effect is achieved, drying, crushing and screening the mixture, adding auxiliary material, drying and crushing the fermented organic material mixing A or B with other auxiliary material and adjusting agent according to the prescription A or B to form the organic composite soil, where the moisture content of the organic composite soil is smaller than or equal to 50%, the organic matter of the dried base is greater than or equal to 40%, the total nutrient content of dried base is 2.2-2.8%, the pH is 5.5-7, the grain size is smaller than or equal to 5 mm and the grain size is 2-4 mm, where the organic composite soil adopts high-temperature corroding agent containing beneficial microorganisms to ferment organic material and adds auxiliary material and adjusting agent to mix. The compound fertilizer is 15-15-15 nitrogen-phosphorus-potassium compound fertilizer. The synergist (0.2-0.5%) is 1000-fold water solution containing silicon, sulfur, calcium, magnesium, trace element iron, manganese, zinc, copper, boron and molybdenum. The strong agent (0.2-0.3%) is paclobutrazol 1000-fold water solution. The physical and chemical indicators are pH of 5.5-7, C/N of 30-40, electrical conductivity of 3-4.5 and water content of 60-75%. The high-temperature corrodent is solid fermenting corrodent containing beneficial microbial population prepared from Actinomyces (40-60%), saccharomycetes, lactic acid bacteria and Bacillus, where the effective viable count is 0.5-100000000 unit/g, the water content of the corrodent is 20- 35%, the pH is 5.5-7.5 and the dosage of the corrodent is 15-20 kg of corrodent added to each 100 cu.m of material. The mushroom scraps are mushroom culture medium of regarding wheat grass as main material. The grass soil mixture is prepared by airing in sunshine and mechanically crushing the material. The volume ratio of the grass soil is 5-10 to 1. 5.