Efforts were paid to obtain nanocarbon/epoxy composites with advanced flame retardancy and mechanical performance, and try to understand the mechanisms. In the first part of the work, when 20 wt% ammonium polyphosphate (APP) in the chosen flame-retardant APP/epoxy composite was replaced by the modified nanodiamond (ND), the tensile properties of the obtained composite successfully improved a lot. At the same time, the obtained composite performed almost as good as the chosen flame-retardant APP/epoxy composite in the limited oxygen index (LOI), UL-94 tests and the second main peak of the heat release rate (P2HRR). More than that, the time to P2HRR (tP2HRR) of the obtained composite was largely expanded compared to the chosen flame-retardant APP/epoxy composite. The smallest FGR (fire growth rate index) and the largest FPI (fire performance index value) of the 8APP-2TND/epoxy composite also suggested the best flame retardancy than any other composites in this work. The mechanisms for the performances in mechanical and flame-retardant properties were studied. In the second part of the work, the introduction of the crushed oxidized carbon nanotube (coCNT) into the epoxy matric was found to effectively increase the LOI value of the epoxy resin. The same time, coCNT strengthened the epoxy matric in tensile modulus, impact strength and storage modulus, without sacrificing other mechanical properties that tested in the present work. The mechanism was proposed, however more detailed works need to be done. More works related to the strengthening of flame retardancy and mechanical performance to epoxy matric by nanocarbons are designed and will be investigated in the following work.