So far there is no an effective method for fast killing of algae and bacteria in the course of conveying ship's ballast water. With a physical method of strong electric-field discharge, O(2) in air and H(2)O in seawater are ionized and dissociated and then dissolved into seawater to generate center dot OH radicals. In the experimental system of 10 t/h, the algae and bacteria are rapidly killed using center dot OH radicals with the low center dot OH concentration of 0.7 mg/L within only 6 s, and D-2 ballast water discharge standard of IMO is realized. Under fluorescence microscope, cell morphological changes such as the disruption of cell membrane, sometimes to the point of cell lysis, has taken place when cells are exposed to a killing dose of center dot OH.