  Polarization detection of X-rays is a non-negligible topic to astrophysical
observation. Many polarization detection methods have been well developed for
X-rays in the energy range below 10~keV, while the detection at 10-30~keV is
rarely discussed. This paper presents a simulation study of a Xe-based gas
pixel detector, which can achieve the polarization detection of X-rays at
10-30~keV. To verify the emission angle distribution of photoelectrons,
different electromagnetic models in Geant4 were investigated. After a necessary
modification by considering the missing factor when sampling the emission
angle, a good agreement can be achieved. Moreover, the detection capability of
20~keV polarized photons was discussed and the modulation factor could be 43\%.
