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With the increase of application of electric and electronic devices in space and nuclear power stations, the polymer insulating materials are inevitably exposed to various kinds of environments. As technology advances, increasing demands on the reliable operation under various operating and environmental conditions are made on materials and components. Therefore, it is important to investigate the influence of radiation on polymeric insulating materials used under the combined environments. This paper describes the effects of magnetic field and gamma-ray irradiation on tracking failure of polybutylene naphthalate (PBN), polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) by applying a HV pulse voltage. PBN, PET and PBT were irradiated in air up to 100 kGy and then up to 1000 kGy with a dose rate of 10 kGy/h by using a 60Co gamma-source. The magnetic flux density (MFD) of the magnetic field was 495 mT and the direction of ExB was 0, 90 and 270 degrees with respect to the sample surface. The effects of total dose of irradiation and magnetic field on the time to tracking failure and discharge quantity were discussed. Obtained results showed that, with increasing the total dose, the time to tracking failure increased with PBN and PET, but decreased with PBT. Under the magnetic field, the time to tracking failure of all the samples were delayed with the relative angles of 0 and 90 degrees, but decreased with the relative angle of 270 degrees. While increasing the total dose, the discharge quantity decreased with PBN and PET, but increased with PBT. Under the magnetic field, the discharge quantity of the samples increased with the relative angles of 90 and 270 degrees, but decreased with the relative angle of 0 degree. In addition, it decreased with the relative angle of 90 degrees for PBT. The experimental results suggest that the chemical structure of the polymeric insulating materials is a dominate factor in the sample reaction to the appli- - ed radiation, which is related to the cross-linking and degradation reaction.