Abstract: Dielectric barrier discharge （DBD） is an important method of generating non-thermal plasma, and DBD generated by nanosecond-pulse is different from that by conventional AC power source. Characteristics of DBD driven by repetitive unipolar nanosecond-pulses in atmospheric air were investigated, the electric parameters were calculated, and the comparison of electric parameters for DBD under AC, microsecond-pulse and nanosecond-pulse excitation was conducted. The relationship between the discharge images and current was obtained, and the discharge mechanism excited by nanosecond-pulse was also analyzed. Some experiment results were acquired, e.g. the measured discharge current exhibits bipolar pulses, which indicating two continuous discharges, and the electric parameters are higher than those under the excitation of AC or microsecond-pulse. Furthermore, with the increase of air gap spacing, the transition from the homogeneous to filamentary discharge is related to the fluctuation of discharge current. Because microdischarge duration and the width of pulse are on the same order under nanosecond-pulse excitation, the microdischarges take place synchronously, and it is difficult for consecutive occurrences on the same location, which has a positive influence on the discharge uniform.