Studying different types of DNA damage induced by ultra-high-dose-rate (UHDR) irradiation is essential for understanding the mechanism underlying the FLASH effect. pBR322 plasmid DNA was irradiated using an electron FLASH beam. The content of each subtype of plasmid DNA was measured via gel electrophoresis, and the extent of DNA double-strand breaks (DSBs) and single-strand breaks (SSBs) under UHDR and conventional-dose-rate irradiation (CONV) was quantitatively compared. Furthermore, by adding the endonucleases Nth and Fpg, the extent of base damage in the UHDR and CONV group was quantitatively analyzed. In addition, the effects of different plasmid concentrations on the damage degree were studied. The induction rates of SSBs (×10