The invention provides a high-density multilayer copper circuit board and a preparation method thereof, wherein the preparation method of the high-density multilayer copper circuit board at least comprises the steps of providing a circuit board substrate; preparing at least two layers of laminated copper conductive lines on the circuit board substrate, and preparing an insulating layer with a through hole between two adjacent layers of copper conductive lines, wherein the two adjacent layers of copper conductive lines are electrically insulated through the insulating layer, and furthermore interlayer metal interconnection is performed through the through hole in the insulating layer. According to the preparation method, based on the single circuit board substrate, a method of laminating multiple layers of conductive lines is utilized, and preparation of the multilayer copper circuit board with smaller thickness and higher reliability can be realized. The preparation method can be used for preparing a thin-line conductive line pattern of which the line width and the line interval range is 2-5 [mu]m. Furthermore a copper etching process or a pattern electroplating copper process or combination of the two processes is utilized for preparing the multilayer copper circuit board. Wiring area can be greatly reduced and wiring density is improved.