Variant selection under specific applied stresses during precipitation of α plates from prior-β matrix in Ti-6Al-4 V was investigated by 3D phase field simulations.The model incorporates the Burgers transfor-mation path from β to α phase,with consideration of interfacial energy anisotropy,externally applied stresses and elastic interactions among α variants and β matrix.The Gibbs free energy and atomic mo-bility data are taken from available thermodynamic and kinetic databases.It was found that external stresses have a profound influence on variant selection,and the selection has a sensitive dependence,as evidenced by both interaction energy calculations and phase field simulations.Compared with normal stresses,shear stresses applied in certain directions were found more effective in accelerating the trans-formation,with a stronger preference to fewer variants.The volume fractions of various α variants and the final microstructure were determined by both the external stress and the elastic interaction among different variants.The α clusters formed by variants with Type2 misorientation ([11-20]/60°) relation were found more favored than those with Type4 ([1055-3]/63.26°) under certain applied tensile stress such as along β.The mechanical properties of different microstructures from our phase field simu-lation under different conditions were calculated for different loading conditions,utilizing crystal plastic finite element simulation.The mechanical behavior of the various microstructures from phase field sim-ulation can be evaluated well before the alloys are fabricated,and therefore it is possible to select mi-crostructure for optimizing the mechanical properties of the alloy through thermomechanical processing based on the two types of simulations.