The present invention relates to hexafluoropropylene oxide polymer composition and a process of preparing ofhexafluoropropylene oxide polymer by an anionic polymerization, and in particular the hexafluoropropylene oxide polymer composition comprises an anionic initiator, a polar solvent, hexafluoropropylene and hexafluoropropylene oxide. The hexafluoropropylene oxide polymer is prepared under particular reaction conditions by using the composition, hexafluoropropylene oxide poylymer prepared by using the composition according to a preparation process herein has a weight average molecular weight (Mw) of 1,500-4,000 at −10 to 20° C.