Abstract: Nanocrystals is a hot topic of poorly soluble drug delivery system under development. Nanocrystals is different from the nanoparticles for drug unloading in polymer materials, and nanocrystals is different from solid dispersion system, in which the drug maintains crystals state. Nanocrystals has a simple preparation process, represents an effective technology in the improvement of solubility and bioavailability of poorly soluble drugs, and has a very promising industrialization application and development potential. In this paper, we retrospect the development history of drug nanocrystals technology, review development of the preparation methods of nanocrystals, and analyze the existing problems to provide a reference to the development of drug nanocrystals preparation.