Using the interface coupling constant Ji and the soft layer thickness Ls as the main variables, the changes of the magnetic moments with the applied field and the hysteresis loops of Nd2Fe14B/α-Fe trilayers, whose easy axes of all layers lie in the film plane, have been investigated. Analysis shows that Ji has significant influence on the magnetic orientation, the pinning field HP and the coercivity mechanism. When Ls is small, HP equals to HN, where the coercivity mechanism transforms from nucleation to pinning as Ji decreases, whereas for large Ls this trend is reversed. The critical thickness, at which the nucleation field and pinning field detaches, decreases as Ji decreases. When the reduced exchange coupling is considered, the rigid composite magnet appears only when Ls is very small. The reduced exchange coupling leads to a sudden change of angle of magnetization at the interface, which results in the change of the behavior of the trilayers from the single-phase one to the two-phase one and in the decrease of HN, whereas HP increases when Ls is larger.