Abstract: Based on thermodynamic non-equilibrium phenomenon, by setting the blend solution poly(lactic acid) (PLA)-poly(ethylene oxide)(PEO)-CHCl₃ in the open system at non-equilibrium conditions to be dried, the compositional gradient phase-separation structures of internal PLA-PEO composites were successfully self-organized. The compositional gradient structure in the composite blend films was characterized by polarized optic microscopy (POM) and the attenuated total reflectance Fourier transformed infrared (ATR-FTIR) spectrum. It is found that the compositional gradient structure is formed in composite at thermodynamic non-equilibrium state. PLA concentrates at the air-side where the energy flows out while PEO at the bottom where the energy flows in, as the system is away from the equilibrium state. The composition of the resulted films distributes gradually along with energy movement direction and presents the tendency of increase with the system away from the equilibrium state. And thermodynamic equilibrium state is the major factor that affects the formation of compositional gradient structure.