The invention relates to an ultrahigh subharmonic quantification method and device based on variable-band aggregation. The method comprises the steps that band aggregation is performed on ultrahigh subharmonics, and an amplitude after ultrahigh subharmonic aggregation is acquired; ultrahigh subharmonic peak change factors after aggregation are calculated according to the amplitude after ultrahighsubharmonic aggregation; and the ultrahigh subharmonic peak change factors after aggregation are utilized to quantify peak attenuation speed of the ultrahigh subharmonics. According to the method, byperforming variable-band aggregation on the ultrahigh subharmonics and utilizing the ultrahigh subharmonic peak change factors calculated according to the amplitude after aggregation to quantify the peak attenuation speed of the ultrahigh subharmonics, guidance can be provided for an ultrahigh subharmonic treatment scheme, and then the power supply quality of a power grid is improved.