The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aeroengine, while the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating. Due to the limitations of laser ignition experiments on the microscopic boundary of the temperature field and the transient propagation mechanism of the temperature field, Molecular Dynamic (MD) simulations and JMatPro calculation are applied in this paper to study the temperature field of Ti-6Al and Ti-48Al. The obtained results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation, and the temperature field of the molten pool is normally distributed from the center to the edge. When the center temperature reaches the critical point of ignition, the extended combustion occurs, and the extended combustion path advances along the direction of the air flow. Compared with Ti-6Al, Ti-48Al alloy has higher fire retardancy under laser ablation. This is due to the higher heat transfer performance of Ti-48Al, which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field. So it is necessary to increase the partial pressure of oxygen, and then reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source. In the aspect of extended combustion path, the boundary heat collection effect of specimens shown by MD models reveal another mechanism affecting combustion expansion path besides the direction of airflow. That is, the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction, resulting in a concentration of heat near the boundary. So the combustion path also tends to expand along this direction.