The invention belongs to the technical field of environmental protection, and particularly relates to a preparation method of an algae biofilm and application thereof in sewage treatment. The preparation method specifically comprises the steps of carrier pretreating, algae culturing, algae domesticating and algae biofilm preparing. The preparation method of the algae biofilm has the advantages that the preparation cost is low, the raw materials are easy to obtain, and the algae biomass is easy to recycle; the prepared algae biofilm can achieve the efficient nitrogen and phosphorus removal effect in sewage treatment, achieves the purpose of general sewage treatment and not only can overcome the defects that in a suspended algae system, the algae density is low, the hydraulic retention time is long, algae and water are difficult to separate, too more suspended solids (SS) exist, the resource recycling rate is low but also has the advantages of reducing immobilization reagent cost, weakening the influences of immobilization reagents on the algae activity, reusing immobilization carriers and the like.