According to the structure figure of the 4-phase asymmetrical coupled inductors (parataxis arranged), the working states are different between symmetrical inductors and asymmetrical inductors. The converter’s performances in steady state and transient state with different degrees of the asymmetric, duty cycles and coupling coefficients are studied by analyzing the working modes of asymmetrical coupled inductors which were used in interleaving and magnetically integrated bidirectional DC-DC converter. The design criterion for the four-phase asymmetric coupled inductors was got. That is, for such asymmetric coupled inductors designed, the parameters could be selected by the formulas and design areas which were given in this paper. At last, the theory was verified with one structure of this kind of inductors for theoretical test.