The invention relates to a method for preparing a boron carbide film by using the electron beam evaporation technology. Boron carbide film material is put in a copple of an electron beam evaporation device, and a substrate which is washed and dried is put on a heating electric furnace of the electron beam evaporation device to lead the substrate to be over the copple, the distance of which is 20 to 30cm from the copple; the filming is executed under the vacuum condition, the filming vacuum degree is more than or equal to 6.0*10<minus 3>Pa, and the temperature of the substrate is controlled between room temperature and 450 DEG C; an electron beam is adjusted to lead the focusing spot on the film material to be smallest; the flux distribution is controlled between 100 to 180mA, and the deposition time is 5 to 120 minutes. The method not only can prepare an amorphous boron carbide film, but also can prepare the boron carbide film with a polycrystalline structure, and also can prepare various boron carbide films with different proportions of B and C components, the surfaces of the prepared boron carbide films are smooth, the films are compact, and the uniformity is good.