NOVELTY - Preparing seedling substrate from green plant waste comprises (i) selecting green plant waste with laminae content of more than 50 wt.%, and crushing, (ii) preparing a compost product by separately adding urea and a microbial fermentation strain into the crushed green plant waste, mixing, and piling, and (iii) preparing seedling substrate by screening the compost product, taking the screened product, after crushing the materials on the sieve, screening, combining the screened products, adding humic acid, pearlite and/or vermiculite into the screened products, and uniformly mixing.    USE - The method is useful for preparing seedling substrate from green plant waste.    ADVANTAGE - The method: reduces the discharge of municipal waste; replaces the traditional seedling substrate with peat or turf which reduces ecological damage; protects peat and turf resource; and is economical.    DETAILED DESCRIPTION - Preparing seedling substrate from green plant waste comprises (i) pre-treating by selecting green plant waste with laminae content of more than 50 wt.%, crushing the waste until the particle size is less than 1 cm, where the green plant waste is plant material including fallen leaves and branches when pruning or intermediately cutting trees and shrubs, lawn lop, abandoned grass, flowers and weeds in gardens and flower buds during natural growth or preserving process of the green plants in urban green lands or suburban forest lands, (ii) preparing a compost product by separately adding urea and a microbial fermentation strain into the crushed green plant waste, uniformly mixing, piling the mixed materials for forming a pile with height of 0.6-1.5 cm and volume not less than 2 m3, then composting the pile for at least 40 days for thoroughly decomposing the material and allowing to stand the pile for 20 days for thoroughly decomposing the material, where the step of composting the pile for thoroughly decomposing the material is as follows: turning the pile for once each day, when the temperature of the pile is 55-65 degrees C, turning the pile for once per 3 days, when the temperature of the pile is less than 55 degrees C, or turning the pile for once per 7 days, when the temperature of the pile is more than 70 degrees C, instantly turning the pile, the urea is agricultural chemical fertilizer urea conventionally supplied in the market, and the amount is 1-2 kg/m3 of the crushed green plant waste, the microbial fermentation strain is produced by Shandong Weifang Zhennong ferment bacteria Co.,Ltd, the amount is 1-1.5 kg/m3 of the crushed green plant waste, and (iii) preparing seedling substrate by screening the compost product by a sieve of 5 mm, taking the screened product, after crushing the materials on the sieve, then screening by the sieve of 5 meshes, then combining the screened products, adding humic acid, pearlite and/or vermiculite into the screened products, and uniformly mixing to obtain a seedling substrate, where the pH in the seedling substrate is 5-7.8, the EC is less than or equal to 0.65 mS/cm, the dry density is less than 0.5 Mg/m3, the wet density is less than 0.8 Mg/m3, the air permeability is greater than or equal to 20%, the moisture content is less than 35%, the germination index is more than 90%, the impurity content is less than 1%, the indexes including the total nutrient and the organic matters meet the requirements of the seedling substrate in national forestry standard (organic matter for greening) LY/ZT1970-2011, the humic acid is lignite, the pH is 4.5-6.5, the content of the organic matter is more than 20%, and the amount of the humic acid is 0-5% of the weight of the screened product, the pearlite is commercially available product and the amount is 0-40% of the weight of the screened product, vermiculite is a commercially available product and the amount is 0-40% of the weight of the screened product.