In power system, series reactor is often used to limit short-circuit current and high-order harmonics in power grid. However, due to the influence of insulation aging, voltage fluctuation, harmonic and external environment, the reactor will produce defects in operation, and even cause accidents such as burning or explosion. Among them, harmonic and temperature rise are the important factors causing insulation defects of reactor. In order to provide an analysis idea of the influence of harmonics and temperature rise on the fault of 10 kV dry-type iron core series reactor for its operation and maintenance, taking a series reactor of cksc-300 / 10-5 as an example, through the establishment of its equivalent circuit and temperature field model, the effect of two factors on the burnout fault of the reactor was analyzed and studied. The results show that the harmonic is not the most direct factor to cause the burnout of the reactor under the appropriate reactance rate; the temperature rise is not one of the direct factors to cause the burnout of the reactor through the simulation analysis of the temperature field, and the influence of other fault causes still needs to be further considered.