The antiferromagnetic layer thickness dependence of the coercivity of the ferromagnetic/antiferromagnetic two-phase system was studied. With mathematical transformations, equivalent anisotropy field and equivalent external field were obtained analytically. In this way, the two-phase system was transformed into a single-phase magnet and its hysteresis loops and coercivities were obtained by using a three-dimensional hybrid hysteresis model. It is shown that the emergence of a peak in the coercivity curve may be related with the competing between the ferromagnetic and antiferromagnetic anisotropy field, or the offset of the equivalent easy axis. The results are discussed and compared with previous work.