The dual-active-bridge(DAB) converter attracts more and more attentions due to its ability of bidirectional power transmission and high conversion efficiency. The adoption of high-frequency transformer provides galvanic isolation, but also brings the possibility of dc bias. In this paper, the causes of dc bias have been analyzed and relevant calculation methods are derived in details. With the calculation methods, the dc bias magnetizing current can be predicted considering the inconsistency of semiconductor switches and driver signals. In other words, if the maximum permitted dc bias of the transformer is given, the range of the inconsistency of semiconductor switches and driver signals can be obtained which helps guide the selection of semiconductor devices and design of the transformer. Therefore, extra flux balancing method can be avoided and the overall cost and volume will be further reduced. Additionally, simulation and experimental results show great agreement with the theoretical analysis.