The interaction of deoxyribonucleic acid (DNA) and hematoporphyrin–gallium (HP–Ga) complex and the damage of DNA under ultrasonic irradiation in the presence of HP–Ga complex were studied by means of UV–vis spectrum, fluorescence spectrum and gelatin electrophoresis. In addition, some influence factors such as ultrasonic irradiation time, HP–Ga complex concentration, ionic strength and solution acidity on the damage of DNA were also considered. Under a certain condition, the damage degree of DNA was enhanced with increasing ultrasonic irradiation time, HP–Ga complex concentration and ionic strength. Whether the pH value was too high or too low, it would be disadvantage to the damage of DNA. Perhaps, these results would be significant for driving sonodynamic treatment (SDT) to the clinic application in the future.