  POLAR is space-borne detector designed for a precise measurement of gamma-ray
polarization of the prompt emissions of Gamma-Ray Bursts in the energy range 50
keV - 500 keV. POLAR is a compact Compton polarimeter consisting of 40$\times$
40 plastic scintillator bars read out by 25 multi-anode PMTs. In May 2015, we
performed a series of tests of the POLAR flight model with 100\% polarized
x-rays beams at the European Synchrotron Radiation Facility beam-line ID11
aming to study thresholds, crosstalk between channels and responses of POLAR
flight model to polarized X-ray beams. In this paper we present the data
analysis method and some analysis results. According the results, POLAR FM has
good polarimetric capabilities.
