A method for film-coating drill bits comprises the steps of: providing a core drill bit; cleaning and further heating the core drill bit; forming an adherent film on the core drill bit; forming a mixing film on the adherent film; and forming a non-crystalline diamond-like film on the mixing film. The finish film-coated drill bit comprises an inner adherence film, a middle mixing film and an outer non-crystalline diamond-like carbon (DLC) film. The mixing film is composed of a non-crystalline diamond-like material and compositions of the adherence film. In the mixing film, the composition of the non-crystalline diamond-like material is higher in a position close to the DLC film.