A GaN nanowall network and InGaN/GaN quantum wells were grown on AlN/Si(111) substrates by molecular beam epitaxy (MBE). The morphology, polarity, structural, and optical properties of the GaN nanowall network were investigated. The lattice constants a0 = 3.193 A and c0 = 5.182 A of the GaN nanowall network were obtained by X-ray diffraction (XRD), indicating that the GaN nanowall network is under low stress. Chemical etching test shows that the GaN nanowall network grown on an Al-polar buffer layer is Ga-polar. Photoluminescence (PL) spectra of InGaN/GaN quantum wells both on a GaN nanowall network and a GaN film were also measured. Different from the InGaN/GaN quantum wells on GaN film, the Fabry-Perot effect is not observed in the PL spectrum of the InGaN/GaN quantum wells on the GaN nanowall network owing to its antireflective porous structure. The emission wavelength gradually blue shifts from 408 to 391nm with the decrease of temperature from 293 to 10 K. The GaN nanowall network grown on a Si substrate is not only compatible with mature Si micromachining technology but also may provide a novel nano-optical device.