The invention belongs to the technical field of printed circuit boards, and discloses a method for machining a PCB copper circuit. The method comprises the following steps that a PCB substrate is immersed into an organic material monomer solution highly diluted through an organic solvent; the PCB substrate is dried and heated to be solidified, and an even bottom layer organic thin film is formed on the surface of the PCB substrate; electroless copper plating, pattern electroplating and flashing erosion are carried out on the surface of the organic thin film in sequence to form the PCB substrate with the copper circuit; the PCB substrate with the copper circuit is immersed into the organic material monomer solution highly diluted through the organic solvent; the PCB substrate with the copper circuit is dried and heated to be solidified, and an even upper layer organic thin film is formed on the surface of the PCB substrate with the copper circuit; an insulating material is arranged on the upper organic thin film layer in a pressing-fit mode to form an insulation layer. Due to the fact that the organic thin film is generated, the smooth degree of the surface of the copper circuit is greatly improved while stable combination of the copper circuit and the substrate is guaranteed, and accordingly the transmission loss of high-frequency signals is reduced while the copper circuit is laid in a high density mode.