The invention discloses a multi-element biological seaweed fertilizer for preventing unclosed rice hulls and a preparation method thereof, belonging to the technical field of rice special fertilizers. Its raw material components are calculated by weight: 10-50 parts of seaweed powder, 2-15 parts of sodium nitrophenolate, 150-450 parts of urea, 150-450 parts of potassium sulfate, 100-400 parts of monoammonium phosphate, calcium magnesium phosphate fertilizer 50-250 parts, calcium silicate 0-50 parts, EDTA chelated zinc 2-15 parts, EDTA chelated boron 2-15 parts, microbial agent 15-40 parts. Compared with the prior art, the product of the present invention is natural, green and pollution-free, and can effectively prevent rice chaff closure; adding medium and trace elements such as calcium, magnesium, sulfur, silicon, zinc, boron, etc., can promote rice chaff closure; Stress resistance and fertilizer use efficiency of crops; improving soil, fertilizing soil fertility, and improving crop quality.