The invention discloses a method for preparing a special alga fertilizer for peanuts, belonging to the technical field of production of special fertilizers for crops. The fertilizer is prepared from urea, monoammonium phosphate, a calcium magnesia phosphate fertilizer, potassium sulfate, sodium borate, EDTA chelated iron, EDTA chelated manganese, EDTA chelated zinc, ammonium heptamolybdate, an alga extracting solution and alga residues. Compared with the prior art, the special high-activity alga for peanuts has the advantages of reasonable proportioning and comprehensive nutrients, and can increase the peanut yield and enhance the peanut quality.