For the need of pulse modulation, an electrode of gas switch whose front shape is annular, is introduced. The fundamental principle that how static electric field around electrode is analyzed by finite element is described. The electrodes whose front shapes are hemisphere, annular and flat with inverted round horn are numerical simulated. These three electrodes' advantage and disadvantage are analyzed and discussed, and it is concluded that the annular electrode can not only ensure that the discharging passage focus on the loop, but also has certain use age. Moreover, with regard to the field strengthen factor, it is shown that this simulation method is practical and reliable by comparison. Finally, the electric performance in high-power pulse circuit is simulated with software PSPICE. The experimental results show that the data from simulation and experiment are identical generally. The gas switch with annular electrode meets the designing demand of steepening and compressing pulse and it has practical application in the high-power pulse modulation circuit.