Domain switching is the main source of nonlinear characteristics in ferroelectrics. According to crystal plasticity theory, the domains and domain switching systems for perovskite- type structure ferroelectrics are de?ned. Considering the traverse motion performance of domain wall, a rather simpli?ed form of evolution law about incremental of volume fraction during domain switching has been developed. The main factors, which exert an in?uence on domain switching, such as material parameters, domain wall motion history, kind of domain switching (180? or 90?) and volume fraction, could be addressed. The hysteresis loops of spontaneous electric polarization as a function of electric ?eld, the butter?y shaped strain versus electric ?eld curve and the platform relations between spontaneous polarization and stress, as well as the longitudinal strain and stress, are well simulated and discussed. Domain switching is the main source of nonlinear characteristics in ferroelectrics. According to crystal plasticity theory, the domains and domain switching systems for perovskite-type structure ferroelectrics are de? Ned. Considering the traverse motion performance of domain wall, a rather simpli? Ed form of evolution law about incremental of volume fraction during domain switching has been developed. The main factors, which exert an in? uence on domain switching, such as material parameters, domain wall motion history, kind of domain switching (180? or 90?) and the volume fraction, could be addressed. The hysteresis electric loops as a function of electric? eld, the butter? y shaped strain versus electric? eld curve and the platform relations between spontaneous polarization and stress, as well as the longitudinal strain and stress, are well simulated and discussed.