Abstract: The experimental apparatus of coaxial water capacitor was set up in microsecond charging condition. Some experiments were done in this device, the voltage of breakdown of coaxial capacitor is measured with positive and negative pulse voltage to charge. Comparing the experimental results with the calculating results, the error of the negative breakdownvoltage is larger and the error of positive breakdownvoltage is less than about 20%. Furthermore, when the resistivity of the water drop to 5MΩ·cm from 13MΩ·cm, the breakdownvoltage of the coaxial water capacitor did not change approximately. The results of experiment are analyzed and are important in design of water dielectric Blumlein pulse forming line with microsecond charging.