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Strain localization influenced by microstructural features has an important effect on mechanical properties of α + β titanium alloy. To address the effect, a microstructure-based finite element model is established. In this model, regions for primary α (αp) and transformed β matrix (βt) are generated from real microstructures of a two-phase titanium alloy (TA15 alloy); the plastic flow behaviors of these two features are determined directly rather than from single phase alloy. A constitutive equation of αp is developed with consideration of dislocation-obstacle interaction, whereas the constitutive equation of βt is determined by nanoindentation tests. Finally, the calculated stress-strain responses of the alloy are verified by experiments. The simulated results show that strain localization bands (SLBs) have two morphologies: short and long-continuous SLBs. Lots of short SLBs appear mainly in βt and αp when the volume fraction of αp is small and moderate, respectively. Long-continuous SLBs appear mainly in αp when the volume fraction of αp is large. With the increase of αp in SLBs, the strength of the alloy decreases while the ductility increases. By decreasing the disparity of strength between αp and βt, the strain gradient in SLBs reduces and the ductility of the alloy increases. [ABSTRACT FROM AUTHOR]