A large number of droplets and their products produced by titanium fire combustion in aeroengine compressor will cause burn through and non-inclusiveness failure of titanium alloy casing. This has shown great harm. In this study， a quantitative evaluation method for titanium fire inclusiveness of compressor was explored based on the mechanism of titanium alloy melt drop ablation and laser ignition technology. A test and evaluation method was established with the characteristic parameters of the melt drop penetration resistance of two configurations of TC4 titanium alloy casing， namely horizontal expansion and vertical drip. Meanwhile， the diffusion behavior of titanium fire and the critical failure conditions under simulated airflow environment were varified by experiments as well. Those results show that the mechanism of titanium alloy droplet burning through the casing lies in the local high heat concentration formed at the droplet contact interface. Under the action of heat transfer， the kinetic energy of the atoms in the base of the titanium alloy cartridge increases rapidly， forming a penetrating liquid phase， and finally causing burn-through， that is， titanium non-inclusiveness failure. When the droplet moves horizontally in the process of extended combustion， it will be affected by some mechanism such as reverse airflow， which will weaken the expansion effect. When the droplet is adhered to the surface of the casing simulation for a long time under the action of gravity or centrifugal force， the heat released is enough to burn through the titanium alloy casing. Its critical thickness is between 1.5-2 mm.