A precise control for the growth of thin film powered by atmospheric pressure atomic layer deposition (ALD) carried out in fluidized bed reactor makes the ultrathin conformal coating of SiO2 on Degussa P25 TiO2 nanoparticles possible. At an operating temperature which can be lowered to room temperature (~27°C), the growth per cycle (GPC) smaller than 1 angstrom (~0.8 Å) allowed us to study on the relationship between the thickness of SiO2 thin film and photocatalytic activities of SiO2 coated TiO2 nanoparticles. Importantly, a considerable enhancement of photocatalytic activity was found which resulted from the formation of crosslinking of Si-O-Ti bonds in the interface between SiO2 and P25 TiO2 nanoparticles as indicated by XPS and FT-IR. The band gap of this interfacial layer can be tuned from 3.10 to 3.23 eV slightly narrower than P25 TiO2’s by varying the number of ALD cycles and the ALD processes at different temperature corresponding to the thickness of SiO2 thin film. Such band gap led to a red-shift of the absorption spectra which means the better absorption of visible light and enhanced the charge transfer from TiO2 to the interface, thereby prevented the rapid recombination of generated carriers. As for the precursors SiCl4 and deionized water vapor, the saturating state of dosing at the first stage of ALD process related to self-limiting reaction can be got after 5 seconds. In addition, annealing could also enable the enhancement of photocatalytic activity via modifying the morphology of interface. Practically speaking, our approach provided a scalable, energy effective and precise method to tune the photocatalytic properties of SiO2 coated Degussa P25 TiO2 nanoparticles which can be both used for photocatalyst about enhancement and pigment about suppression.