For a dual-active-bridge type three-phase single-stage isolated AC-DC converter topology, to suppress DC bias of transformer current, the conventional modulation strategy regulates transformer current by limiting the three-phase shift angles but leads to a restriction of system transfer power. In this paper, a new modulation strategy for a dual-active-bridge type three-phase single-stage isolated AC-DC converter topology is proposed. By introducing a new initial phase-shift angle, the modulation can decouple adjacent switching cycle transformer current without limiting the range of the conventional three-phase shift angles so that the power transfer capacity of the system is unrestricted. In addition, the system power transfer characteristic of proposed modulation strategy is also analyzed in this paper. The effectiveness of proposed modulation is validated by simulation.