The microstructure and mechanical properties of WSTi3515S alloy after various heat treatments and thermal exposure treatments were researched. The results indicate that different heat treatments below 850 oC have little effect on microstructure and mechanical properties of the alloy. When the heat treatment temperature is 950 oC, the microstructure of the alloy obviously changes; however, the room-temperature mechanical properties have no change, which indicates that WSTi3515S alloy holds better microstructure and performance stability. After the heat treated samples are thermal exposed at 570 oC for 100 h, the strength of the alloy increases and the elongation sharply decreases. During the thermal exposure process, there is a small quality of precipitations in the alloy and they mainly distribute at grain boundaries. The precipitation at the grain boundaries is the main reason for the decreased elongation of the alloy after thermal exposure