The invention discloses a multi-element biological alga fertilizer for preventing and treating rice spike develop abnormality, and a preparation method thereof, and belongs to the technical field of special fertilizers for rice. The fertilizer comprises, by weight, 10-50 parts of alga powder, 2-15 parts of compound sodium nitrophenolate, 150-450 parts of urea, 150-450 parts of potassium sulfate, 100-400 parts of monoammonium phosphate, 50-250 parts of calcium magnesium phosphate, 0-50 parts of calcium silicate, 2-15 parts of EDTA chelated zinc, 2-15 parts of EDTA chelated boron, and 15-40 parts of a microbiological agent. Compared with fertilizers in the prior art, the fertilizer of the invention is natural and green, has no pollution, can effectively prevent and treat the rice spike develop abnormality, can promote the rice spike chaff closing due to the addition of medium trace elements of calcium, magnesium, sulfur, silicon, zinc and boron, improves the stress resistance of crops and the fertilizer utilization rate, improves soil, cultures fertility and improves the quality of the crops.