Carbon nanotubes (CNTs) and graphene attract enormous research attention for their outstanding material properties along with molecular scale dimension. Optimized utilization of the graphene based materials in various application fields inevitably requires the subtle controllability of their properties according to a specified target application. In this presentation, our recent research works associated to nitrogen-doped graphene based nanomaterials will be presented. Substitutional doping of CNTs and graphene with nitrogen (N) heteroelement could be achieved via pre- or post-synthetic treatment. The resultant N-doped CNTs and graphene demonstrate tunable workfunction, modulated charge carrier density and remarkably enhanced surface activity, including catalytic behavior, which could be employed for many different graphene based functional nanostructure or heterostructure formation. N-doped CNTs could be hybridized with metallic nanoparticles to accommodate plasmonic properties with charge selective carrier transport, which can be utilized for the effective enhancement of device efficiency of organic and perovskite solar cells. Various catalytic oxides or other ceramics, such as amorphous molybdenum sulfides, can be directly deposited at the surface of N-doped graphene based materials without any intermediate adhesive layer for high performance hybrid photocatalysts or electrocatalysts for oxygen reduction or hydrogen evolution reaction. N-dopant sites can initiate damage-free unzipping of graphene plane to greatly enlarge the surface area of N-doped CNT array, whose facile carrier transport along the highly crystalline unzipped nanoribbon structure can be utilized for ultrahigh power supercapacitors and so on.