Polyimide (Pp-matrix composite films containing nitrogen (N) doped graphene sheet have been fabricated by employing in-situ polymerization and their microstructure has been investigated by the small angle X-ray scattering (SAXS) and scanning electron microscopy. The N doped graphene (NG) possess excellent dispersion within the PI matrix, and forming strong links with the polymer to facilitate load transfer. The PI/NG composite films exhibit improved mechanical properties than that of the pure PI film. The tensile strength of the integrated PI/NG composite films with 0.1 wt% loading is 15% greater, and the elongation at break is 230% greater than comparable properties of pure PI film. This approach provides a strategy for developing high performance graphene-polymer composite.