The invention discloses a method for preparing special organic soil for vegetable seedling culture and belongs to the technical field of soilless culture. The organic soil is prepared from aged agaricus bisporus sward mixture, a mixed organic material of vinegar residue and cassava residue, which are subjected to composting and fermenting, coco coir, river / pond sludge or frozen soil or humus soil, plant ash and vermiculite. The method comprises the following steps: firstly, carrying out composting and fermenting treatment on the vinegar residue and the cassava residue by adopting a beneficial microbe containing zymocyte agent, then, respectively drying the aged agaricus bisporus sward mixture and the mixed organic material of the vinegar residue and the cassava residue, which are subjected to composting and fermenting, in the air, and crushing into granules, of which the grain size is smaller than 5mm; then, adding the coco coir, the river / pond sludge or frozen soil or humus soil, the plant ash, the vermiculite and a compound fertilizer; and then, thoroughly stirring the raw and auxiliary materials, uniformly mixing, then, bagging, weighing, packaging and warehousing. The organic soil is granular solid, of which the appearance is dark-brown or black-brown, and is odorless. The special organic soil for the vegetable seedling culture, prepared by the method, is loose in texture and high in nutrient, does not float during watering and is applicable to the majority of vegetable plug seedling culture.