Microstructure and mechanical properties were researched under different heat-treatment conditions for damage tolerance TC4-DT alloy. The relation between the different microstructure parameters with mechanical properties was analyzed, and the influence of different cooling rates on fracture toughness of TC4-DT titanium alloy was investigated. The result shows that the heat-treatment can adjust the microstructure parameters, including the content of primary α, the dimension of β grains and the dimension of lamellar α, which can affect the properties of TC4-DT alloy. The factors that influence the properties were mainly analyzed theoretically, and the fracture surface was observed