As a technology of separation and purification, crystallization plays a vital role in diverse industries such as inor-ganic salt, pharmaceutical, and food industries, which has a huge impact on purity, crystal polymorph, crystal morphology, and particle size distribution offinal products. In the past few decades, with the rapid advancement of experimental approaches and molecular simulation methods, considerable advances in the interpretation of crystallization mechanisms have been obtained, promoting the investigation and understanding of crystallization theories greatly. In this review, the advances of pharmaceutical crystallization theories in recent years from the perspectives of nucleation and crystal growth are summarized and discussed. Two thermodynamic models that are helpful in the study of the crystallization mechanisms will be introduced. In this section, the perturbed-chain statistical associating fluid theory (PC-SAFT) and a chemical-potential-gradient model will be introduced, which have been successfully applied in pharmaceutical solubility prediction, the research of disso-lution mechanism as well as dissolution kinetics analysis. These two models are expected to be applied to the study of pharmaceutical crystallization process and mechanism. Furthermore, molecular simulation based on the interaction between particles can provide structural information, thermodynamics, and dynamics properties of complex systems at the molecular level, like intermolecular interaction and surface adsorption energies. Appli-cation and some shortcomings of molecular simulation, especially molecular dynamics simulation, in the field of pharmaceutical crystallization will be expounded.