Due to the advantages of high efficiency, low mass, modularization and high power density, the step-up resonant converter is widely adopted in providing kV-level high voltage for the ion propulsion power supply. As a key part of the resonant converter, the resonant tank topology is evaluated in this paper. Based on the characteristics of the high-voltage resonant converter, a selecting criteria for the resonant tank is proposed. Applying the criteria to the 2-element, 3-element, and 4-element resonant tank topologies, the candidate for high-voltage application can be recommended. Then, the selected topologies are compared based on the relationship between voltage gain and frequency. The analytical results show that the gain valley could be more easily founded in the 4-element resonant tank compared with others, thus it is more suitable for the high-voltage application.