The invention relates to a high-temperature-resistant, water-oxygen-resistant and low-infrared-emissivity composite film for a ceramic-based composite material and a preparation method. The high-temperature-resistant, water-oxygen-resistant and low-infrared-emissivity composite film for the ceramic-based composite material is of a single-layer complex-phase structure, and the surface of a target object is covered with the composite film when the composite film is used; and the thin film is a continuously formed high-temperature conductive composite thin film and comprises two main components, wherein a high-conductivity metal material is used as a low-infrared-emissivity component, and an environment barrier coating material for the ceramic-based composite material is used as a protection component. After process optimization, the emissivity of the composite film of 2-22 microns can be less than 0.1 after the composite film is used in a high-temperature air environment of 1000 DEG C for 2 h, the composite film has excellent performances of low emissivity, high temperature resistance, water and oxygen resistance and the like, and the preparation process is simple and the operation is easy.