The material of porous nano-TiO2 was prepared with a new preparation method. The relations between the crystalloid and the size of TiO2 nanograin and the technics conditions were studied. The control of TiO2 nanograin was discussed initially. It has very high photocatalytic activity. The degradation rate of the methyl orange solutions (50 mg L-1) which were decomposed by nano-TiO2 in the irradiation of the ultraviolet highvoltage mercury lamp whose main wavelength is 365 nm only in 17 min was above 99.6%. After stopping irradiation, there is a degradation dark-reaction whose reaction rate is rapid at first and then slow down. The standpoint that in the anatase TiO2 there are thimbleful rutile TiO2 which could bring the cooperation photocatalysis degradation and improve its photocatalytic activity was first put forward. (c) 2005 Elsevier B.V. All rights reserved.