The thermo-optic effect and infrared optical properties of VO2 nano array were studied in order to obtain high quality optical material widely used in the field of smart windows. Reflectance and transmittance spectra of VO2 nano array at different duty ratios were calculated with a modificatory Sellmeier dispersion model and equivalent refractive index of two-dimensional periodic structure. The vanadium nano array was deposited on the glass substrate by magnetic reactive sputtering with the mask of porous alumina, and then VO2 nano array was formed by annealing under air condition. Its microstructure and optical properties were characterized by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and spectrophotometer. The results show that the phase transition temperature of VO2 nano array with duty ratio 0.83 drops to 43 oC and its optical contrast between the metallic and semiconducting states at 1700 nm is 29%, which exhibits a significant thermochromic property. Contrast to VO2 film, the transmittance of VO2 nano array has been noticeably improved. The decrease of phase change temperature and enhancement of optical properties demonstrate that VO2 nano array with decent duty ratio is a competitive candidate material for smart windows