It is proposed to grow VO₂ nanoparticles on the surface of porous silicon using a chemical vapor transport deposition method to form a porous silicon-based VO₂ nanoparticles composite structure for improving the sensitivity of porous silicon to NO₂ gas at room temperature. The size of VO₂ nanoparticles is altered by varying the VO₂ deposition pressure and research is conducted on its effect on the gas sensitivity of the porous silicon-based VO₂ nanoparticle composite structure at room temperature. The microscopic morphology, phase, and crystal structure of the composite structure are characterized and analyzed using a field emission scanning electron microscope, X-ray diffractometer, energy spectrometer, and transmission electron microscope. The experimental results demonstrate that the composite structure obtained at the deposition pressure of 330 Pa has the highest room temperature sensitivity (13.15) to the mole fraction of 5×10^-6 NO₂, which is 5.95 times the sensitivity of porous silicon, and has good selectivity. The excellent NO₂ gas sensitivity is due to the surface activity enhancement of VO₂ nanoparticles with small particle size and the formation of a wider depletion layer between the smaller VO₂ nanoparticles and porous silicon, thus improving gas sensitivity. This research will help to improve the application of porous silicon in NO₂ gas sensor.