A novel nanocomposite thin film material of SnO2/WO3 metal oxide compound doped by multi-walled carbon nanotubes (MWCNT) and its corresponding gas sensor were prepared by radio frequency (RF) reactive magnetron sputtering. The surface composition and chemical elements of the thin film material were respectively analyzed and validated by X-ray diffraction (XRD) and photoelectron spectroscopy (XPS). The influencing factors of gas sensing properties were studied and the test results of gas sensor were analyzed. The results indicated that the detection using the composite material gas sensors for low concentration NO2 toxic gas could be greatly improved by MWCNTs which were doped on the mixed oxides matrix. A possible mechanism explaining the behaviour of the thin film gas sensor was introduced.