In light of the increasing diameter requirements for polystyrene-polyvinyl alcohol (PS-PVA) bilayer hollow microspheres in inertial confinement fusion (ICF) physics experiments, a 3D spin-coating method based on planar spin-coating was proposed in this paper as a means of overcoming the limitation of the traditional emulsion encapsulation method in preparing microspheres of a millimeter scale and above. A three-dimensional spin-coating apparatus was devised and constructed for the generation of PVA films in situ on the surface of millimeter-scale ( approximately 1500 μm ) monodisperse PS microspheres through solvent evaporation. The interaction between the PS microsphere surface and the highly alcoholysis degree PVA was enhanced by oxygen (O₂) plasma treatment, which facilitated the spreading of PVA solution on the surface of PS microsphere. In combination with the optimization of the key parameters, the morphology and thickness of the PVA liquid film were effectively controlled online. The homogeneity of the PVA film layer was improved and the millimeter-scale PS-PVA bilayer hollow microspheres were obtained.