Abstract: The influence of elevated temperature holding time(t_β) on grain growth, microstructure transformation and mechanical properties in heat affected zone of fine grained Ti-6Al-4V alloy with equiaxed crystal has been investigated using thermal simulation testing machine.Results show that grains in coarse grained region have been coarsened seriously and the intracrystalline α' is composed of orthogonally oriented martensitic plates which have a substructure containing predominately twins with longer t_β;Grain growth tendency is relatively little and its morphological features of intracrystalline α' present lath martensites which have a substructure containing predominately dislocations with medium and shorter t_β;Continued increases in t_β results in a reduction in the hardness of coarse grained region;Finer grains, intracrystalline α' martensites having dislocation substructure induced by shorter t_β result in higher mechanical properties than martensitic plates which have substructure containing twins with higher t_β in coarse grained region.