Abstract: Breakdown caused by bubbles is a critical technical problem for the application of PEF(Pulsed Electric Field). At present, theories about gas bubbles breakdown under water can not explain the breakdown phenomenon of uniform electric field under 70 kV/cm. In order to solve this problem, the gas breakdown experiments between the metal plate electrode and the aqueous electrode are designed in this paper. The breakdown voltage of the air gap with the liquid electrode is obtained, which proves the influences of the cathode types and the repetition frequency pulse parameters on it. The gas-breakdown phenomenon of short-gap with aqueous electrode (less than 1 cm) at atmospheric pressure was studied by equivalent experiments. The relationship between the internal electric field of bubble and the bubble shape factor as well as gas-liquid dielectric constant under uniform electric field was obtained. According to the research above, it is considered that the complete breakdown of the PEF treatment chamber is caused by the bubble breakdown in the aqueous solution, which is affected by the secondary electron emission coefficient γ of the cathode. The breakdown field strength of bubbles in water is predicted. This work presents vital references for designing PEF treatment chambers.