The surface oxidation of titanium alloy is widely used to improve wear and corrosion resistance and interfacial compatibility. In this study, a surface heat source with a Gaussian distribution was employed to simulate the temperature field changes during the surface oxide layer preparation on a titanium alloy (Ti6Al4V) using an infrared laser. First, the simulation results of the temperature distributions on the titanium alloy surface and thickness with 500 W laser power (39.8 W/mm² power density) and 15 mm/s scanning speed were compared with the experimental results, verifying further the effectiveness of the finite element model. Next, the verified model was used to study the influence of the laser power, scanning rate, and repeated scanning interval on the temperature field. The simulation results reveal that the line energy increased when the laser power was increased and the scanning rate was decreased. Consequently, the temperature field on the surface and along the thickness increased as a whole. Under the same line energy, a higher surface temperature and a similar internal temperature could be obtained under both high energy and scanning speed because of the energy accumulation on the titanium alloy surface. Moreover, the maximum surface temperature of the titanium alloy increased with the scanning interval reduction.