The photochromic of nano-TiO2 with different crystals and the hydrous TiO2 in the glycerol environment were systematic studied in this paper. Experimental results showed that，amorphous TiO2（hydrous TiO2）has the most obvious discoloration，while rutile nano-TiO2 has no obvious coloration，the degree of discoloration of anatase nano-TiO2 is between rutile and amorphous，the mixed crystals（rutile and anatase）nano-TiO2 is weaker than anatase but stronger than rutile. The samples were characterized by X-ray photoelectron spectroscopy（XPS）and UV-visible（UV-vis），and the results indicated that the Ti3+ existed in the colored sample and the visible absorption spectrum of samples were significantly different before and after colored. The double-injection mechanism and the small polaron model were used to describe the photochromic mechanism of TiO2. The electron-hole recombination rate effected on the Ti3+ formation and the effects of glycerin for TiO2 photochromic phenomenon were investigated in this paper. The formation rate of Ti3+ decreased with the increasing of the electron-hole recombination rate，which leaded to the weakening of the color. The glycerin could promote the photochromic of TiO2..