The invention discloses a polyethylene bio-carrier and an application of the polyethylene bio-carrier to sewage treatment. Linear low-density polyethylene serves as a main frame material, the polyethylene, sugarcane residue and activated carbon are mixed according to proportion, and die-casting molding is implemented. The sugarcane residue is flushed by ethyl alcohol, dried and crushed. The activated carbon is selected from common powdery activated carbon in the market. The cost of the bio-carrier is greatly reduced, and the bio-carrier is applied to aerobiotic and anaerobic biological treatment processes. The bio-carrier is high in bio-film culturing speed, process stability is enhanced, starting time of a process is obviously shortened, sludge amount in drained water is obviously reduced, and the drained water is close to clear, so that later drainage treatment is facilitated.