Polybutylene isophthalates (PBI) end-capped with N-ethyl-pentadecafluorooctanamide were synthesized from dimethyl isophthalate, 1,4-butanediol, and N-(2-hydroxyethyl)-perfluorooctanamide with fluorine monomer content from 0 to 5 mol %. The results demonstrated that there was an obvious gradient drop of fluorine concentration from the film surface down to the inner bulk, and the enriched perfluoroalkyl segments covered the rough disordered crystalline topography of PBI, leading to greatly decreased roughness values of fluorinated films. Moreover, the film with only 3 mol % fluorine monomer content exhibited the surface tension of 16.7 mN/m, even lower than that of polytetrafluoroethylene (18.5 mN/m), indicating that the fluorinated groups not only enriched on the film surface but also tended to orient the CF(3) group upward. This study is of significance for further understanding the effects of polymeric structural factors on the migration ability of fluorine in the polymer film.