This paper presents a new application of the phase field method. Two-dimensional phase field simulations of domain switching in the crack tip vicinity of a crack embedded in a ferroelectric single crystal, which was subjected to mechanical and electric loading, have been carried out. Khachaturyan-Shatalov (KS) theory  was adopted to account for the elastic energy. The domain switching zones induced by the mechanical and electric loading were plotted. The stress field near the crack tip was also plotted to investigate the effect of domain switching on the crack. The obtained domain switching zones are in good agreement with reported theoretical predictions and experimental observations. The stress field shows that the positive electric field inhibits while the negative field promotes the crack propagation.