The gas discharge and plasma oscillation between the electrodes of high-voltage alternating current arc generator are studied, and the nanosecond pulsed phenomenon in the gas discharge process is observed at atmospheric pressure. Electron accumulation phenomenon under the action of alternating electric field is described by using a function. Based on the equation of electron fluid motion and Maxwell equations, the discharge voltage between the electrodes is depicted theortically. Theoretical and experimental results are consistent with each other basically, and the electron density is estimated to be 1.3 1012/m3.