The invention relates to a method for machining an overlong concentric ladder through hole on an ordinary boring machine through a lengthening boring cutter rod. The method comprises the steps that 1, all parts of a workpiece are subjected to rough machining, and the periphery of the workpiece is subjected to finish machining; 2, the workpiece is subjected to alignment and clamping; 3, the lengthening boring cutter rod is composed of a taper shank section and a bare shaft section, the bare shaft section is provided with a plurality of boring cutter grooves in the longitudinal direction, and the shaft end of the bare shaft section is sleeved with a sliding sleeve; 4, a tailstock bracket is installed on the ordinary boring machine; 5, the lengthening boring cutter rod penetrates through the concentric ladder through hole, one end of the taper shank section is connected with a spindle of a machine tool, one end of the bare shaft section is installed on the tailstock bracket through the sliding sleeve, and the sliding sleeve and the tailstock bracket are tightly locked; a boring cutter body is installed, and try cutting is conducted; and 7, after try cutting is qualified, all the parts of the concentric ladder through hole are subjected to finish machining to reach the requirement of a drawing. According to the method for machining the overlong concentric ladder through hole on the ordinary boring machine through the lengthening boring cutter rod, existing machine tool auxiliaries are fully utilized, and the situation that the bore hole machining precision is influenced due to sinking of the lengthening boring cutter rod is avoided; and the effect that the size, the form and position tolerance and the surface roughness of the overlong concentric ladder through hole machined on the ordinary boring machine meet the requirements is ensured, so that the machining cost is reduced, and the production efficiency is improved.