We proposed a method of polarization shaping in the focal region with the polarization modulation of incident light. By using an iterative optimization based on a vectorial diffraction calculation with the help of the fast Fourier transform, we can tailor the polarization structure in the focal plane. This provides a novel way to control the vectorial feature of the focal volume with the help of polarization tailoring, which is different from the method using wavefront shaping. The capability of polarization-only modulation on the incident light is demonstrated by optical experiments.