Abstract: The stress and strain properties of \langle 001 \rangle oriented PMN-0.32PTrelaxor ferroelectric single crystals have been investigated. Obtainedresults show that the stress and strain behavior along \langle 001 \ranglecrystallographic direction is different from that of the ferroelectricpolycrystal. Polarization rotation models are developed to explain theobserved behaviors of PMN-0.32PT. Based on the experimental phasetransformation mechanism of ferroelectric single crystal, a constitutivemodel of ferroelectric single crystal is proposed based micromechanicalmethod. In the model, the phase transformation systems on 8 possible slidingplanes are characterized by a viscoplastic law. The behavior offerroelectric single crystal is then derived from phenomenalcrystallographic theory through the transformation strain on sliding planes.The developed model has been applied to simulate the experimentalstress-strain curve of \langle 001 \rangle oriented PMN-0.32PT. It is shown that thedeveloped model can faithfully capture the key characteristic of theobserved constitutive behavior of \langle 001 \rangle oriented PMN-0.32PT.