Abstract: Acetanilide，hexane diacid and potassium hydrogen phthalate were used as additives to improve polyvinyl chloride (PVC) crystallinity. From the analyses of Fourier transform infrared spectrum，differential scanning calorimetry and wide angle X-ray diffraction，it is found that all of the three organic compounds were compatible with PVC to some extent，but the compatibility between PVC and hexane diacid was less satisfactory. Acetanilide and hexane diacid，potassium hydrogen phthalate could improve PVC crystallinity. For all samples，PVC chains in the crystalline phase were of all- trans extended syndiotactic configuration，and acetanilide and hexane diacid could make the conformation of chains in the amorphous phase more stable than pure PVC，while potassium hydrogen phthalate decreased the stability of chain conformation in the amorphous phase. The three additives did not influence PVC crystal system，and all samples were in the orthorhombic system.