A topology of series connection of resonant DC-DC converter featuring inherent automatic voltage and current balance is proposed in this paper. The input-series-output-parallel DC-DC converter has voltage and current unbalance issues due to the parameters mismatch, which will threaten the safe operation of the converter. To address the above-mentioned problems, a topology of series connection of resonant DC-DC converter with auto voltage and current balance capability is derived. The foundation of this derived topology stems from combination of the series connection of the resonant DC-DC converter and the flying-capacitor-based three-level structure. In the proposed topology, voltage balance is achieved through the utilization of the flying capacitor, while the resonant current balance relies on the series interconnection of the transformer’s secondary side. A comprehensive investigation into the voltage and current balance mechanism is revealed that demonstrates the voltage and current auto-balance is achieved by the flying capacitor without any additional active components or control loops. Furthermore, generalized rule of derivation is analyzed, which can derive additional converters for more potential applications. Finally, an experimental prototype was built and tested. The experimental results show that the voltage and current can be well shared, which demonstrate the feasibility of the proposed topology.