In this work, the effects of fluorine treatment of polyimide thin film on surface and dielectric characteristics were studied using X-ray photoelectron spectroscopy (XPS) and dielectric constant, respectively. And, their thermal and mechanical properties of the polyimide film were characterized by thermogravimetric analysis (TGA) and tensile strength, respectively. The fluorine content of the polyimide film was increased with increasing the amount of the treatment gas, resulting in decreasing the dielectric constant of the film. It was explained that the replacement of fluorine led to the decrease of the local electron polarization of polyimide, or to the increase of the free volume which can be attributed to the relatively large volume of fluorine. Nevertheless, the fluorination didn’t significantly affect thermal or mechanical properties of the polyimide film under a mild condition in this system.