NOVELTY - Preparing growing medium, comprises crushing the greening plant waste, domestic sludge and poultry excrement, adding domestic sludge or poultry excrement in the crushed greening plant waste, adding urea, uniformly mixing, detecting, composting in cones to obtain compost product, detecting pH, electrochemical (EC), density, ventilation property, total nutrition, organic substance, nitrogen, phosphor and potassium of the compost product, selectively adding humic acid, perlite and/or polyacrylamide, uniformly mixing, and detecting to obtain growing medium.    USE - The growing medium is useful as soil for roof, suspending and vertical three-dimensional greening (claimed).    ADVANTAGE - The prepared medium can replace nature soil to plant plants (claimed) and satisfy the requirement of roof, suspended and vertical three-dimensional greening to soil fertility and soil structure, and has water and fertilizer retaining property. The method enhances the recycle and reuse of wastes; and has excellent social, economic and biological benefits.    DETAILED DESCRIPTION - Preparing growing medium, comprises: (a) pre-treating the greening plant waste, domestic sludge and poultry excrement by crushing the greening plant waste to obtain the crushed greening plant waste with particle size of less than 2 cm, respectively the moisture content and carbon-to-nitrogen (C/N) ratio of the crushed greening plant waste, domestic sludge and poultry excrement; (b) preparing compost product by adding domestic sludge or poultry excrement in the crushed greening plant waste, where the addition amount of the domestic sludge or poultry excrement is 5-30% of the weight of the crushed greening plant waste, adding urea (0-0.8% of the weight of the crushed greening plant waste), uniformly mixing, detecting the C/N ratio of the mixture being 25-30 with a moisture content of 40-60%, composting into cones of 0.60-1.5 m in height and at least 2 cm3 in volume, composting for 20-40 days to obtain compost product with a moisture content of less than 38%, where the composting treatment is as follows: re-stacking for one time when the temperature in the cone is 55-60 degrees C, re-stacking for one time within 3-5 days when the temperature is 60-65 degrees C, re-stacking at once when the temperature is higher than 70 degrees C, and re-stacking for one time within 7-12 days at a cooling period when the temperature is less than 55 degrees C; and (c) preparing growing medium by detecting the pH, electrochemical (EC), density, ventilation property, total nutrition, organic substance, nitrogen, phosphor and potassium of the compost product of the step (b), selectively adding humic acid (0-5% of the weight of the compost product), perlite (0-40% of the weight of the compost product) and/or polyacrylamide (0-5% of the weight of the compost product) based on the requirement of national forestry standard 'organic medium for greening' LY/T1970-2011 to the growing medium, uniformly mixing, and detecting where the impurity is less than 1% by weight, the pH value is 5-8, the EC value is 0.35-1.5 mS/cm, moisture content is less than 35% by weight, the organic substance content is greater than or equal to 15 g/kg, the total nutrition (nitrogen + phosphate pentoxide + potassium oxide) is greater than or equal to 1.5%, the dry density is 0.1-0.8 Mg/m3, the wet density 1.2 mg/m3, the ventilation property is more than 20% and the germination index is more than 80%, to obtain the growing medium, which meets the growing medium requirement of 2011 published national forestry standards organic medium for greening.