The invention discloses a microorganism fertilizer for promoting crop growth and a preparation method therefor. The microorganism fertilizer comprises the components in parts by weight: 100 parts of plant stalks, 0.08-0.16 part of 5A-hydroxyl laxogenin, 0.04-0.10 part of theobromine, 60-80 parts of chitosan hydrochloride, 0.8-1.2 parts of bacillus subtilis bacterium, 6-10 parts of lactobacillus powder, 4-8 parts of yeast powder, 8-20 parts of potassium dihydrogen phosphate, 6-10 parts of ferrous sulfate, 10-15 parts of calcium carbonate, 1-3 parts of magnesium chloride, 1-3 parts of molybdate, 1-3 parts of zinc sulfate, 1-3 parts of manganese sulfate and 1-3 parts of boric acid. The microorganism fertilizer disclosed by the invention comprises 5A-hydroxyl laxogenin and theobromine, the two components have mechanisms that promote growth, and compound use of the two components can further play synergy, so that the crop growth is significantly improved. In addition, after the chitosan hydrochloride is dissolved into soil, animal and plant residues and trace metal elements are decomposed, thereby transforming into nutrients of plants, improving plant immunity, and promoting plant health.