A stable apremilast (represented by formula I) crystal form II free of solvates, a preparation method therefor, a pharmaceutical composition and pharmaceutical uses thereof, as well as a mixed crystal of the crystal form II and a crystal form B and a preparation method therefor. The 2θ±0.2 of an X-ray powder diffraction (XRPD) pattern of the apremilast crystal form II has five characteristic absorption peaks: 11.2, 13.2, 13.5, 13.8, and 14.7； and a Differential Scanning Calorimetry (DSC) thermogram shows a single absorption peak at 150±3 °C. The activity of the crystal form II is not lower than that of the crystal form B, and the thermodynamic stability of the crystal form II is superior to that of the crystal form B. The preparation methods are simple to operate, and a used crystal solvent is safe and is easy to be removed.
