The invention provides a PCD (polycrystalline diamond) milling cutter. The milling cutter comprises a cutter body and a milling cutter blade, wherein the cutter body is made of hard alloy or steel; a positioning surface, a welding surface and a cuttings discharge groove are arranged on the cutter body; the milling cutter blade is fixedly connected with the welding surface; the positioning surface is perpendicular to the welding surface; a cross section of the cutter body is round; the milling cutter blade is formed by machining a PCD composite piece with a polished surface and is provided with a front cutter blade parallel to the bottom surface of the cuttings discharge groove; a cutting edge, a flexible belt, a first back cutter surface and a second back cutter surface are arranged on the outer edge of the milling cutter blade in sequence downwards from a front cutter surface of the milling cutter blade; and the flexible belt is the polished surface of the PCD composite piece. According to a method for machining the PCD milling cutter, the polished surface of the PCD composite piece is reasonably utilized, and the front cutter surface, the second back cutter surface and the first back cutter surface are formed by machining in sequence through laser cutting, so that the PCD milling cutter can machine workpieces with high surface smoothness.