The work aims to fabricate a composite nanostructures featuring in size selective photocatalytic function, which can maintain photocatalytic property of TiO2, and reduce the photocatalytic corrosion behavior to organic macromolecular materials and organic substrates, so as to expand range of application of photocatalytic materials. One-pot method was used to hydrolyze with P25 as core by means of TEOS and prepare porous TiO2 (P25) nano-particles in composite core-shell nanostructure (P25@SiO2) covered by SiO2. TEM, XRD and BET tests verified that the P25@SiO2 exhibited good dispersion and high specific surface area (about 528 m2/g). Photocatalytic performance test confirmed that this core-shell composite had a size selective photocatalytic effect, i.e., small molecule nitrogen oxide gas (NOx) could enter TiO2 core through SiO2 shell pore passage and further was decomposed by over 90%; a small molecule organic methylene blue could also penetrate into the core parts through SiO2 shell pore passage and was oxidized and thereby decomposed, while macromolecular organic Ponceau 4R was effectively insulated and was not decomposed. The aging experiments showed that organic substrate PET membrane coated with P25@SiO2 was not restrained by oxidization and ageing. On the contrary, compared with the bare organic substrate PET membrane, the organic substrate coated with core-shell nanostructure had better UV resistance due to protective effect of the shell layer. The size selective photocatalytic composite core-shell material can be coated on the surface of various organic substrates, providing them with certain catalytic function. Meanwhile, owing to the protective effect of SiO2 shell, the corrosive effect on substrate is inhibited. In addition, the core-shell materials can be added in various coating materials as function addition material, endowing coatings with photocatalytic properties such as air purification and self-cleaning function without damaging some organic compounds in the coatings. Therefore, the P25@SiO2 materials have very good application prospects.