Nanopaticles of TiO2 mixed crystals (anatase phase and rutile phase) are prepared by detonation method. Morphologies and structural phase transformation behaviors of the as-prepared TiO2 nanopaticles are investigated for different annealing temperatures (600 ℃ and 720 ℃) and durations of annealing time (1, 2, 3.5, and 5 h). The structural phase transformation process and transformation mechanism are also discussed within the framework of the thermodynamic theory. Results show that with the increase of the annealing temperature and annealing time, the particle size of the detonation-prepared TiO2 nanoparticles increases gradually and the relative content of rutile phase in the TiO2 mixed crystal nanopaticles is improved. Compared with the TiO2 nanoparticles prepared by the conventional methods, the mean growth rate of rutile phase is obviously slower than that of anatase phase at the same annealing temperature and annealing time. It is obvious that the temperature at which the anatase phase completely changes into the rutile phase is lower than that of the TiO2 nanoparticles prepared by using other methods. These results are helpful for realizing the control of particle size and phase transformation of TiO2 nanoparticles. Meanwhile, the results can also provide us the theoretical and experimental bases for mass production of TiO2 nanoparticles in the future.