(1) processing a substrate material of a substrate holder to obtain a surface that is separated from diamond films, wherein the substrate material of the substrate holder is processed in any of the following ways:

Way I: using a first material as the substrate material, performing surface polished processing, and forming a first nucleation layer on a surface of the substrate material to obtain the substrate holder, the first material being a material that does not react with carbon at the vapor deposition temperature of diamond, and the material of the first nucleation layer is selected from diamond, amorphous carbon, silicon carbide, silicon, germanium, beryllium, and combinations thereof;

Way II: using a second material as the substrate material, performing surface polished processing, and forming a second nucleation layer to obtain the substrate holder, the second material being a material that softens or melts at the vapor deposition temperature of diamond, and the material of the second nucleation layer is selected from carbon, silicon, silicon carbide, silicon nitride, and combinations thereof;

Way III: processing the surface of the substrate material and forming a loose layer and a third nucleation layer thereon in sequence to serve as the substrate holder, a material of the loose layer is selected from amorphous carbon, amorphous silicon, diamond micro-powder, silica micro-powder, aluminum oxide micro-powder, and combinations thereof; a material of the third nucleation layer is selected from diamond, amorphous carbon, silicon carbide, silicon, germanium, beryllium, and combinations thereof;

(2) using a plasma chemical vapor deposition method to form a diamond film layer on the surface of the substrate holder, wherein the plasma chemical vapor deposition method uses a multi-energy sources coupled plasma, and the plurality of energy sources are 2, 3, or more kinds;

(3) post-processing the diamond film layer to remove impurity material on the diamond surface and a nucleation layer and/or stress layer with inconsistent properties of a main body of the diamond film.