The dielectric response of -oriented 0.68PMN-0.32PT single crystal under dc electric field has been investigated. The characteristics of phase transition under temperature and dc electric field are provided. When electric field is above 2.3kV/cm, abnormal phase transition is induced by temperature and electric field, which corresponds to the phase transition from rhombohedral to orthorhombic ferroelectric phase. With increasing dc electric field, the stable temperature region of orthorhombic phase is expanded. The electric field-temperature (E-T) phase diagram of -oriented 0.68PMN-0.32PT single crystals is presented. The polarization rotation in -oriented single crystal is discussed.