The polarization microscope and scanning electron microscope were used to study the surface structure and the cross section of the grafted copolymer of polytetrafluoroethyene—styrene—fumaric acid in this paper. In the range of the experimental temperatures (19~40℃), when the radiation intensity is higher than the critical radiation intensity, the grafting takes place on the surface of film. On the contrary, the grafting proceeds in the mass. Under the surface grafting conditions, the spheric particles are formed on the surface of grafting copolymer. It was found that the inner layer is the grafted copolymers of polytetrafluoroethyene—styrene—fumaric acid and the outer layer the homopolymer of styrene—fumaric acid. The outer and inner layers are linked by chemical bonds. The main contribution to the adhesive strength is made by outer layer. The grafting process and mechanism and effect of grafting conditions on surface structare have been discussed considering the diffusion and permeation of monomers. In the case of surface grafting, the adhesive strength is found to be above 100 kg/cm,2,. On the contrary, the adhesive strength is found to be lower 40 kg/cm,2, when grafting took place throughout the PTFE substrate.