The invention discloses a granular compounded organic fertilizer which comprises the following raw materials in parts by weight: 60-80 parts of livestock manure, 30-50 parts of manioc wastes, 12-25 parts of sugar plant filter mud, 5-10 parts of medicine dregs, 40-60 parts of white mud, 1-5 parts of potassium fulvic acid, 5-10 parts of an inorganic fertilizer, 1-5 parts of biological bacteria, 5-10 parts of fermentation bacterial and 1-5 parts of a compound aid, wherein the weight ratio of nitrogen and phosphorus to potassium in the inorganic fertilizers is 15:(3-8):(8-12). The invention further provides a preparation method of the granular compounded organic fertilizer. As the granular compounded organic fertilizer is prepared from agricultural wastes through two times of fermentation, wastes can be turned into wealth, and the problem of organic matter environment pollution can be solved; due to the addition of inorganic fertilizer components, and appropriate proportions of elements of nitrogen, phosphorus and potassium, a good fertilizer effect can be achieved, and nitration absorption of plants can be promoted; the prepared granular compounded organic fertilizer is good in organic fertilizer effect, is capable of loosening soil and powerfully ensures that high-yield, safe, high-quality and efficient agricultural products can be produced.