A method for improving the non-linear load charging capability of a synchronous generator set by adding a shafting flywheel includes: a rotating shaft of a prime motor of the synchronous generator set is extended, the cross section of the tail end of the extended rotating shaft is processed into a regular hexagon for installing flywheel sheets, holes which are regular hexagons are arranged at the centers of the flywheel sheets and sleeved on the rotating shaft for installation, fixing parts of the flywheel sheets are formed by a shaft sleeve of the rotating shaft and a welding vertical ring, screw holes are arranged on the flywheel sheets and the vertical ring, and the flywheel sheets are fixed with the vertical ring through bolts. The method for improving the non-linear load charging capability of the synchronous generator set by adding the shafting flywheel improves the capability for charging non-linear load of the synchronous generator set, the flywheel easy to install and demount is added on a shafting of the generator set, so that inertia of the power source is increased, the stability and power supply quality of a power supply system are increased, and the effect of stabilizing the frequency is achieved.