The asymmetric three-level/two-level three-phase dual-active bridge converter(ADAB3) is a popular topology suitable for high-power DC-DC isolation conversion. However, due to passive component tolerances, the ADAB3 converter experiences undesirable phase current imbalance. This paper investigates the issue of inductor current imbalance in the ADAB3 converter and proposes a current balancing strategy using vector analysis. In this strategy, the required compensating phase-shift angle between the primary and secondary side voltages are calculated to achieve balanced phase currents. Simulation results demonstrate that the proposed current balancing strategy significantly improves the phase current imbalance caused by passive component tolerances.