Aiming at the breakage of tool and low precision of the machined surface in the high-speed milling process of titanium alloy, damage mechanics is used to reveal the formation mechanism of tool fatigue breakage during the milling and determine the critical condition of tool breakage. Cutting edge chipping caused by random impact fracture during the evolution of tool damage is the main failure form of tool fatigue breakage. Based on continuous damage mechanics, fatigue crack growth theory and sliding crack energy balance equation, the crack growth law of tool material is studied under different cutting impact, and the initial damage value and critical damage value of tool material fracture based on the interval method are obtained. And the impact fracture limit conditions of the end mill edge are established including cutting parameters, material hardness, tool damage, tool wear, and cutting impact, which provide a theoretical basis for determining the cutting parameters. A titanium alloy milling experiment is carried out to define the impact damage morphology of the tool in different states after the tool is damaged. The obtained tool safety area range is verified, and the research results provide parameter optimization for the high-speed and high-efficiency milling titanium alloy process.