Abstract: As a necessary transformer equipment, the safe and economic operation of the transformer is essential.In order to study the influence of harmonics on transformer insulation aging, this paper first theoretically analyzes the relationship between the hottest spot temperature and the harmonic content, and its influence on the three indicators of transformer thermal aging rate, aging acceleration factor and remaining life, and then combines the relationship between the hottest temperature and the harmonic content under the three cooling methods of natural oil circulation, forced oil circulation, and forced oil circulation guidance, the curves of transformer thermal aging rate, insulation aging acceleration factor, remaining life and total harmonic current distortion rate are drawn, and the influence of harmonics on transformer insulation is quantified.