Embodiments of the present disclosure provide a method of fast optimization and compensation for volumetric positioning errors of rotary axes of a five-axis CNC system machine tool. The method comprises: establishing a volumetric positioning error model; forming an error database containing 12 geometrical error vectors; constructing a volumetric positioning error compensation table; establishing a compensation value optimization model; completing an iterative optimization of compensation values of volumetric positioning errors; generating a volumetric positioning error compensation file for a CNC system to complete compensation for the volumetric positioning errors; and updating the error database, detecting linkage trajectories of the rotary axes, and setting a linkage trajectory positioning error threshold, and guaranteeing accuracy by iteratively implementing detection, optimization, and compensation.