Dual-phase high-strength titanium alloy has the properties of high specific strength and good toughness, which have resulted in its gradual use in the fields of oil and gas well engineering. The elevated-temperature service environment of deep strata is its key research direction. In this paper, the strength and fracture mechanism of a new type of α + β-phase titanium alloy tubing material in its service-temperature range are studied. Its fracture mechanism changed at 130 °C to 150 °C, from normal-stress ductile fracture to quasi-cleavage fracture formed by β-phase voids, which induced microshear, which significantly reduced the elongation of the material and accelerated the rate of yield strength decline with temperature. This mechanism provides a new guiding idea for the design of the microstructure and element content of dual-phase high-strength titanium alloy. For titanium alloy materials in service within the temperature range of the fracture mechanism transition, which is between 130 °C and 150 °C, reducing the void-inducing factors in the β-phase or reducing the content of the β-phase to avoid microshear failure should be considered.