The thermal stability of Ti14, a novel α+Ti2Cu burn resistant titanium alloy, after semi-solid forging (SSF) with different deformation amount from 45% to 75% was investigated. Effects of deformation amount on the thermal stability were analyzed. The results show that the deformation amount significantly affects the morphology of precipitates and grain size, leading to change of thermal stability. With the deformation amount increasing, the strength of Ti14 alloy after thermal exposure decreases first and then increases, and the plasticity was improved. When the deformation amount was 45%, the microstructure consisted of coarse grains and strip-like Ti2Cu precipitates in the grain boundary. As deformation amount increases to 75%, the microstructure changed to refined grains and granular or/and short rod-like Ti2Cu, inducing the improvement of strength and plasticity. Fracture analyses show that the fracture has lots of tearing ridges for small deformation amount; when the deformation amount reaches 75%, the fracture are mainly dimples. It indicates the precipitates and grain size determine the thermal stability of Ti14 alloy together.