The present invention provides a preparation method of the reduced and N-doped graphene oxide comprising the steps of preparing the mixed solution containing graphene oxide (GO) and tetramethylammonium hydroxide (TMAH) (step 1) and heating the mixed solution prepared in step 1 (step 2). The preparation method of the reduced and N-doped graphene oxide of the present invention can provide the fully reduced and N-doped graphene oxide even at a low temperature by using tetramethylammonium hydroxide, the tetra ammonium salt, as a nitrogen dopant. According to this method, N-doping level can be regulated by controlling the mixing ratio of graphene oxide and tetramethylammonium hydroxide. Further, this method does not need any additional additive to prepare the reduced and N-doped graphene oxide, so that it is a pro-environmental method that facilitates the mass-production simply with solution process.
