  Thomson scattering of intense laser pulses from relativistic electrons allows
us to generate high-brightness and tunable-polarization X/{\gamma}-ray pulses.
This paper demonstrates the polarization control of the Thomson scattering
source experimentally. The polarization of X/{\gamma}-ray is related to
incident polarized laser beams, which is controlled by rotating a quarter-wave
plate. In the experiment, the polarization of X-ray is determined by recording
the spatial distribution of scattered photons, produced by X-ray irradiating on
a target. According to modulation curves analysed from experiment results, the
conclusion is that the polarization of Thomson scattering source is tunable and
controllable. Meanwhile, stokes parameters of X/{\gamma}-ray whose energy
varies between tens of keV and MeV are simulated. Considering the paraxial
photons, it is showed that the polarization is nearly the same value in a wide
range of X-ray energy according to simulation results.
