We propose an orientation-dependent polarization manipulation by Cherenkov radiation (CR) in a silicon-on-insulator (SOI) waveguide with a metasurface. By putting an electron bunch passing near the SOI waveguide, CR excites the fundamental TE-like mode with ultra-high mode purity. The spin state of the decoupled light is determined by the direction of the electron motion, and the maximum magnitude of the normalized Stokes polarization parameter
S
3
approaches
±
1
, corresponding to the right and left circularly polarized light. This Letter provides a new, to the best of our knowledge, way to achieve CR with spin angular momentum in an SOI waveguide and offers a platform to study the interaction between an electron and light with nanostructures on-chip.