The invention discloses a PCB depth-control machining method and a device thereof. The method comprises the following steps of: preparing a soft board and a hard board, wherein the soft board is a compacting board and provided with a depth-control area to be machined, and a plurality of first air holes which are perforative at both sides are arranged in the hard board; arranging a PCB to be machined between the soft board and the hard board, wherein the soft board and the hard board fully cover the PCB, the cover ranges of the soft board and the hard board both extend out of the periphery of the PCB, and a space for accommodating the PCB is formed between the soft hard and the hard board; vacuumizing the space formed between the soft board and the hard board by taking the first air holes as air faucets; and carrying out depth-control machining on the evacuated PCB. The invention can realize the depth-control machining effect with high precision and is basically inexistent of the problem that some areas can not be machined.