Investigations on the interconnection between the polarization rotation and crack propagation are performed for [110]-oriented 74Pb(Mg1/3Nb2/3)O3-26PbTiO3 relaxor ferroelectric single crystal under electric loadings along [001]direction. The crystal is of predominantly monoclinic MA phase with scatter distributed rhombohedral(R) phase under a moderate poling field of 900 V/mm in[001] direction. With magnitude of 800 V/mm, a through thickness crack is initiated near the electrode by electric cycling. Static electric loadings is then imposed to the single crystal. As the applied static electric field increases, domain switching in the monoclinic MA phase and phase transition from MA to R phase occur near the crack. The results indicate that the crack features a conducting one.Whether domain switching or phase transition occurs depends on the intensity of the electric field component that is perpendicular to the applied electric field. Investigations on the interconnection between the polarization rotation and the crack propagation are performed for [110] -oriented 74Pb (Mg1 / 3Nb2 / 3) O3-26PbTiO3 relaxor ferroelectric single crystal under electric loadings along [001] direction. The crystal is of predominantly monoclinic MA phase with scatter distributed rhombohedral (R) phase under a moderate poling field of 900 V / mm in [001] direction. With magnitude of 800 V / mm, a through thickness crack is initiated near the electrode by electric cycling. As imposed on the single crystal. As the applied static electric field increases, domain switching in the monoclinic MA phase and phase transition from MA to R phase occur near the crack. The results indicate that the crack features a conducting one. WHhether domain switching or phase transition occurs depends on the intensity of the electric field component that is perpendicular to the applied electric field.