Unlike　inorganic　quantum　dots,　fluorescent　graphene　quantum　dots　(GQDs)　display　excitation-dependent　multiple　color　emission.　In　this　study,　we　report　N-doped　GQDs　(N-GQDs)　with　tailored　single　color　emission　by　tuning　pi-conjugation　degree,　which　is　comparable　to　the　inorganic　quantum　dot.　Starting　from　citric　acid　and　diethylenetriamine,　as　prepared　N-GQDs　display　blue,　green,　and　yellow　light　emission　by　changing　the　reaction　solvent　from　water,　dimethylformamide　(DMF),　and　solvent　free.　The　X-ray　photoelectron　spectroscopy,　ultraviolet-visible　spectra　results　clearly　show　the　N-GQDs　with　blue　emission　(N-GQDs-B)　have　relatively　short　effective　conjugation　length　and　more　carboxyl　group　because　H2O　is　a　polar　protic　solvent,　which　tends　to　donate　proton　to　the　reagent　to　depress　the　H2O　elimination　reaction.　On　the　other　hand,　the　polar　aprotic　solvent　(DMF)　cannot　donate　hydrogen,　the　elimination　of　H2O　is　promoted　and　more　nitrogen　units　enter　GQD　framework.　With　the　increase　of　effective　pi-conjugation　length　and　N　content,　the　emission　band　of　N-GQDS　red-shifts　to　green　and　yellow.　We　also　demonstrate　that　N-GQDs　could　be　a　potential　great　biomarker　for　fluorescent　bioimaging.