The invention discloses a fabrication method for backdrilling of an asymmetric printed circuit board. The method comprises the following steps: (S1) carrying out a front process; (S2) laminating an outer copper foil layer and an inner core plate layer, drilling a through hole on an outer layer, carrying out outer copper precipitation and metalizing the through hole; (S3) carrying out full-plate electroplating, fabricating an outer circuit pattern layer and carrying out pattern electroplating; (S4) carrying out first backdrilling on the through hole; (S5) carrying out silkscreen solder resisting after etching the outer layer; (S6) molding; (S7) carrying out second backdrilling on the through hole; and (8) carrying out a post-treatment. Twice backdrilling is carried out; the first backdrilling is carried out until the previous layer of a target depth and a target layer is not drilled; second backdrilling is carried out after a large semi-finished product of the circuit board is cut into small circuit board units; the relative board warpage value of the cut circuit board is reduced; the backdrilling progress can be relatively well controlled; the problem that the backdrilling depth of the asymmetric structure printed circuit board which is greater than or equal to 4mm in thickness is difficult to accurately control is effectively solved; and scrapping of the circuit board caused by the overlarge backdrilling depth is avoided.