Vapor phase infiltration (VPI) derived from atomic layer deposition (ALD) enables inorganic materials to nucleate and grow within the free volume of polymers, which has shown promising prospects in the field of composite solid polymer electrolytes (CSPEs). However, there are only a few types of metal oxides that can be incorporated into the polymer matrix by VPI, let alone binary metal oxides, due to the limited knowledge of the VPI synthesis process. To combine the merits of different metal oxides, we investigate the VPI method to prepare ZnO-Al2O3 composites in poly(ethylene oxide) (PEO). When the introducing order is Al2O3/ZnO (AZO), due to the extremely high reactivity of trimethyl aluminum (TMA) with PEO, VPI-Al2O3 will accumulate near the surface of PEO. The surface Al2O3 layer inhibits the further diffusion of the diethyl zinc (DEZ) into the PEO matrix, leading to weak polymer–filler interactions and limited improvement of the Li+ conduction. In the incorporation order of ZnO/Al2O3 (ZAO), the moderate reactivity of DEZ renders the uniform distribution of VPI-ZnO within PEO, and the following TMA can both react with PEO and VPI-ZnO particles near the surface of PEO, which not only preserves the interactions between VPI-ZnO and PEO but also better inhibits the growth of lithium dendrites. The incorporation order plays a crucial role in the morphology and composition of binary metal oxides synthesized by VPI.