The influence of pre aging heat treatment on microstructure and mechanical properties of coarse grained β titanium alloy has been studied in this paper. The pre aging heat treatment could serve as a precipitation step to provide uniform dispersed precursors for secondary α phase precipitation, and then leads to the dense, finely and homogenous distribution of secondary α phase. Prolonging of the pre aging time results in the finer scale of secondary α phase. The pre aging heat treatment strongly affects the mechanical properties of β titanium alloy. Within a coarse grain condition, the strength tested in this work is about 1340MPa when single aging at 550oC. However, the strength achieves to 1760MPa when pre aging at 350oC before 550oC, which increased by more than 30% compares to single aging. The micro hardness of the alloy also be improved markedly by pre aging. The effect of pre aging time on mechanical properties is that the prolonging of the pre aging time leads to the increase of strength and micro hardness, but the ductility is sacrificed, which is mainly due to the refinement of secondary α phase.