The invention discloses an organic-inorganic compound fertilizer for landscape greening plants and a preparation method of the compound fertilizer. The organic-inorganic compound fertilizer for landscape greening plants is prepared from the following raw materials in parts by weight: 45-65 parts of municipal sludge, 20-30 parts of coconut oil cake, 10-15 parts of corncob, 16-22 parts of furfural residue, 12-18 parts of beer grain meal, 10-15 parts of edible mushroom leftovers, 7-13 parts of pepper meal, 5-10 parts of bits of wood, 4-8 parts of coal slag, 5-10 parts of waste molasses, 8-14 parts of spoiled milk, 10-15 parts of bamboo shoot shell, 5-10 parts of wormcast, 6-12 parts of volcanic mud, 5-10 parts of sea mud, 4-8 parts of medical stone powder, 3-5 parts of germanium stone powder, 9-18 parts of modified attapulgite, 5-10 parts of turfy soil, 4-8 parts of paper ash, 3-6 parts of crab shell powder, 10-15 parts of carbamide, 5-10 parts of monoammonium phosphate, 8-16 parts of calcium superphosphate and 2-4 parts of potassium chloride. The compound fertilizer has more nutrient elements, balanced in nutrient and capable of remarkably improving the utilization rate of the fertilizer and the rapid growth of the plants. The compound fertilizer also has the characteristics of stable, long and comprehensive fertilizer efficiency and has functions of improving soil properties, improving the soil fertility and reducing soil-borne disease; after the fertilizer is applied for one time, the demands of the plants on various nutrients can be met, so that the fertilizer does not need to be applied repeatedly, thus the labor cost is saved.