In this paper, the acetone solvate of candesartan cilexetil was preferentially crystallized from the acetone solution by cooling crystallization and was characterized by combination methods of X-ray powder diffraction (XRPD), C-13 nuclear magnetic resonance (NMR), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), Forier transform infrared (FTIR), Raman spectroscopy, and dynamic vapor sorption (DVS). The polymorphic transformation among two polymorphs (form I and form II) and acetone solvates of candesartan cilexetil was investigated, respectively. By regulating the initial solution concentration and composition of solvent mixture (water/acetone), form I or acetone solvate could be obtained. With the aid of in situ Raman spectroscopy, the kinetics of solvent-mediated transformation (form II -> acetone solvate) and solid-state transition (acetone solvate -> form II) were systematically studied at different temperatures. The results show that the mechanism of solid-state transformation of acetone solvate to form II depends on one-dimensional diffusion.