V₂O₅ has the highest oxygen state in vanadium-oxygen systems and is the most stable member of the series of vanadium oxides. V₂O₅ is an n-type semiconductor at room temperature with wide bandgap between 2.2 eV and 2.4 eV, high absorption coefficient, and unique orthorhombic layered structure. Multi-walled carbon nanotubes have unique high mechanical strength, high electrical conductivity, high thermal stability and good electrochemical properties, usually considered as a p-type semiconductor. The synthesis of p-type multi-walled carbon nanotubes with n-type V₂O₅ will form p-n heterojunction, which increases the Schottky barrier, mobility and quantum effect, and can achieve excellent optoelectronic properties which is conducive to the preparation of optoelectronic devices, such as ultra-high-speed switches, high-frequency and high-speed components, and solar cells. Ions have been doped into V₂O₅ thin films to improve their optical and electrical properties, and the results show that doping other elemental ions to fill gaps or replace atoms in the lattice can effectively enhance the optical and electrical properties of thin films by forming additional donors or acceptors to facilitate the interband jumps of the phase transition process. In this paper, V₂O₅/MWCNT nanocomposite films were prepared on quartz substrates by sol-gel method and post-annealing process due to its advantages of being environmental friendly, inexpensive, and requiring simple fabrication. Firstly, 0.5 g V₂O₅ and 0.33 g MWCNT power were progressively added to the 40 ml H₂O₂ solution at room temperature while the solution was continuously stirred. After stirring for 3 hours, continued stirring in 75 ℃ water bath until the exothermic reaction was complete, the multi-walled carbon nanotubes were ultrasonically dispersed in the solution at a certain molar ratio of V₂O₅ to multi-walled carbon nanotubes for 0.5 hour. The solution was continued to be stirred in the water bath for more than 1 hour until the composite gel was formed. Finally, the V₂O₅/MWCNT composite film was fabricated on quartz substrates by the homogenizer and annealed at 400 ℃ for 2 hours in the furnace. The surface morphology, structure, chemical composition and elements, and optical-electrical properties of the V₂O₅/MWCNT composite films have been investigated. The SEM image of the surface morphology of the V₂O₅/MWCNT composite film measured by scanning electron microscopy clearly shows that the composite film has a fine and uniform surface with good crystallinity and lamellar nanostructure. The profiles of V₂O₅/MWCNT composite films measured by X-ray diffractometer obviously confirm the presence of V₂O₅ in the composite films. X-ray photoelectron spectra demonstrate that the V₂O₅/MWCNT composite films contained oxygen, vanadium, carbon and no other elements. The ratio of the areas of C_1s and V_2p confirms that there is no loss of material content in the preparation process of the composite film. Raman spectra clearly manifest the presence of MWCNT in V₂O₅/MWCNT composite films. The photoelectric properties of the composite films are analyzed by using spectrophotometry and other instruments. The results show that the doping of MWCNT broadens the band gap of the composite films to 2.42 eV which is wider than that of films without doping of MWCNT, and its resistance is decreased from 52.38 MΩ to 0.97 MΩ when the temperature is increased from room temperature to 270 °C with 5 ℃/min rise rate, which has a change of nearly two orders of magnitude. In the wavelength range of 600~1 200 nm, the average transmittance of the composite film is 58%, and the transmittance variation before and after the phase transition is changed up to 2%. The transmittance is increased under the applied voltage from 0 to 7 V. The composite films have been tested undergoing many high and low temperature cycles with stable performance. Its photoelectric properties have both stable and great reversible thermotropic photoelectric properties, which are expected to be applied in the fields of optoelectronic integration, new photoelectric devices and sensors.