Mesoporous anatase crystal-silica nanocomposites with three-dimensional (3D) uniform and tunable intrawall mesopores connecting the mesochannels have been successfully prepared using the approach of first synthesizing titania-silica nanocomposites with ordered two-dimensional hexagonal mesochannels via "synchronous-assembly" of inorganic precursors with surfactant, then "extracting silica". The uniform intrawall pores can be finely tuned in 3.6-5.6 nm by the strategy of adopting a large amount of silica in the walls, a very high crystallization temperature and mild silica extraction. The 3D interconnectivities of the mesochannels increase with extraction, but the mesostructures are retained intact. The average size of uniform anatase nanocrystals is 11.2 nm. This method is moderate, simple and facilely reproducible. The diffusion efficiencies of methylene blue (MB) in the mesostructures elevate with the intrawall mesopore size. The transient steady-state concentrations of center dot OH radicals rise fast with the intrawall pore size. The degradation rate of MB on the representative photo catalyst possessing large intrawall mesopores is extremely high (0.372 min(-1)), which is as high as 7.3 times that on the parent material, even up to 38.8 times that upon P25 photocatalyst Our results clearly illustrate that the large intrawall mesopores play an overwhelming role in the increments of activities, while the matched adsorbability play an important synergetic role. Additionally, our photocatalysts are quite stable and reusable. Such results have not been seen in the literature till now. Furthermore, this approach is generally applicable to other metal-oxides-based materials, opening up a new avenue to rationally design and prepare mesostructures with 3D large intrawall mesopores, suitable adsorption and unexpected photocatalytic performances.