The work aims to study the compatibility, crystallographic characteristics and evolution of water vapor barrier properties of polylactic acid/poly propylene carbonate (PLA/PPC) blends with different condensed structures and broaden the application scope of blends in the packaging field. Three kinds of PLA/PPC blends with different condensed structures (amorphous form, α¢ crystalline form and α crystalline form) were prepared by blending method and different heat treatment processes and then characterized and tested by FT-IR, DSC, OM, SEM, XRD, DSC and water vapor permeability test. Although there was certain compatibility, PLA and PPC showed thermodynamic incompatibility on the whole. The crystal structure of the crystalline PLA/PPC blends changed from α¢ to αcrystalline form when the heat treatment temperature increased from 80 ℃ to 130 ℃. The results of water vapor permeability test showed that the crystalline blends with α crystalline form had the best barrier performance to water vapor. At the same time, the water vapor permeability coefficients of the blends with three different condensed structures were qualitatively given in the order of amorphous form >α¢ crystalline form > α crystalline form. Blends with different condensed structures have different structures and water vapor barrier properties. The excellent water vapor barrier properties of α crystalline form are mainly attributed to the higher regularity of macromolecular chains, stronger van der Waals force between chains and longer path of water vapor diffusion. It is an effective method to adjust the structure and properties of PLA/PPC blends by controlling the condensed structures.