Abstract: It is proved by lots of experiments that, domain switching is the main reason for the nonlinear and hysteresis constitutive behaviors of ferroelectric ceramics. And a large number of studies have been conducted on the microscopic domain switching behaviors of BaTiO3 single crystals. Through direct stroboscopic observation, the forward and sideway motion of 180º domain wall is measured, and the formula of velocity is given. In order to derive the evolution equation of the volume fraction of domain switching, a square domain switching model is developed according to the relation between the domain wall velocity and applied electric field. The proposed model is compared with the nonlinear behavior of BaTiO3 single crystals subjected to mechanical loadings and electric field loadings. It demonstrates that the model presented can predict the typical nonlinear the nonlinear hysteresis of ferroelectrics under electrical or mechanical loading.