Abstract: TC18 titanium alloy was heat treated by BASC (β annealing+slow cooling) and BASCA (β annealing+slow cooling+aging),respectively.The relationship between the microstructure and mechanical properties of TC18 titanium alloy was studied by tensile and impact properties tests,optical microscope and scanning electron microscope.The results show that the change trend of metallographic structure of the alloy is close after the two groups of process treatment.The main difference is that a large number of secondaryα_s phases are precipitated in the structure after aging treatment.After BASC treatment,the strength and plasticity of the alloy decrease with the increase of heating temperature.After BASCA treatment,the strength of the alloy shows the opposite trend with the BASC process.After two groups of process treatment,the impact toughness of the alloy decreases with the increase of heating temperature.After BASC treatment,the overall impact toughness of the alloy is higher.When the BA temperature is located in the two-phase region,the tensile and impact fracture morphologies of the two processes are mainly dimples.When the BA temperature is located in the single-phase region,the tensile fracture morphologies of the two processes are mainly crystalline,with obvious tearing edges,and obvious cleavage steps appear in the impact fracture morphology.