Inertial electrostatic confinement (IEC) fusion device has been investigated as a compact fusion source to generate byproducts of fusion reactions for many applications. However, the IEC fusion device still has insufficient fusion reaction rate and stability issues in high power operation. In this work, a cylindrical IEC device is designed and discharge voltage and current at various pressures and geometries are studied to understand their effect on discharge. From this result, three key features is observed and discussed: 1) discharge voltage in IEC device increases with lower transparent cathode at the identical operating pressure, 2) high voltage and current discharge can be obtained with higher operating pressure at the identical pd value. 3) high voltage discharge without decrease of operating pressure can be obtained by considering limit length of cathode diameter in IEC device. Based on these results, it is supposed that transparency and size of cathode in an IEC device can be optimized for high voltage and current discharge with relatively high operating pressure to increase fusion reactions of beam-cathode surface and beam-background gas besides ion-ion fusion reaction in continuous IEC discharge. Consequently, these results can be reflected on design of a high-yield fusion sources.