The invention discloses a method for machining a central hole of a crankshaft. The method comprises the following steps that 1, a crankshaft blank is clamped and fixed; 2, shaft necks at the two endsof the crankshaft are clamped through chucks; 3, the beating values of all the shaft necks of the crankshaft are adjusted through the chucks, so that the crankshaft reaches the technically required numerical value; 4, a turning tool is adopted to cylindrically turn the shaft necks; and 5, an assistive device provided with a center drill is adopted to be fixed to a lathe tailstock, the crankshaft is rotated, and the center drill feeds to drill the central hole.