Cocrystals, as an excellent solid state to improve the physicochem. properties of active pharmaceutical ingredients, have always been discussed together with solvates since the definition of cocrystals was proposed.However, investigation and discussion of the boundary between cocrystals and solvates have not been common.In this work, aiming at betulin (BE)-a natural product with multiple pharmacol. activities, we designed its polymorphism and cocrystal screening experiments with different liquid organic solvents and solid cocrystal coformers (CCFs) that possess low and high m.ps., resp.Afterward, a hemihydrate, a new solvate with benzyl alc., and two new cocrystals of BE with phenol (PHE), and 3-hydroxybenzoic acid (3-HBA) resp., including their single crystal structures, were designed, prepared, and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and other solid-state anal. methods.A special thermal property for pharmaceutical cocrystals was found in cocrystal BE-PHE, i.e., it possesses an exact CCF loss process, which is different from cocrystal BE-3-HBA but is similar to the solvate of BE.To explain this phenomenon, theor. calculation studies were performed by mol. electrostatic potential surface anal., electron d. difference anal., energy decomposition anal., and energy framework anal. to realize an in-depth study of the sites, quantities, and energy of the intermol. interactions between BE and different coformer mols.Results indicated that the fewer interaction sites and the small interaction energy between BE and PHE mols. are the possible reasons for the unusual thermal properties of cocrystal BE-PHE.This finding also proved that the structural features of cocrystals can affect their physicochem. properties greatly.