In this study, non-hydrogenated oxygen-doped diamond-like carbon (DLC) films were grown by femtosecond laser, and the influence of oxygen atmosphere on the infrared (IR) properties of the films was investigated. The evolution of the properties of oxygen-doped DLC films at the microscale was determined by investigating their doping content, atomic bonding, and crystal structure. The results show that the oxygen atmosphere increases the diamond-phase content and reduces the absorption of the DLC films, thus increasing their IR transmittance. The refractive index of the films can be freely controlled by the oxygen atmosphere, which provide a suitable method for the design of multilayer optical films. The oxygen in the environment does not change the amorphous structure of the DLC films and does not hinder their IR transmittance. A model is proposed for the rearrangement of the atomic bonds in the carbon films in the oxygen atmosphere, which is of benefit to the research on oxygen-doped DLC films and provides theoretical analysis and a practical basis for improving the anti-reflective protection of IR windows by DLC films.