A　novel　g-C3N4　nanosheets　embedded　with　C3N4　QDs　nanocomposites　(QD@CNNS)　was　prepared　by　simple　oxidation　using　hydrogen　peroxide　and　UV　light　irradiation.　This　nanocomposite　exhibits　more　stable　and　stronger　electrochemiluminescent　(ECL)　behavior　compared　with　CNNS.　Coupling　this　nanocomposite　with　Fc-labeled　aptamer,　a　signal-on　aptasensor　for　platelet　derived　growth　factor　BB　(PDGF-BB)　is　fabricated.　Initially,　the　Fe-labeled　aptamer　binds　onto　QD@CNNS　via　pi-pi　conjugation　and　electrostatic　interaction,　quenching　ECL　emission　from　QD@CNNS.　The　introduction　of　target　efficiently　recovers　the　ECL　signal　by　the　formation　of　PDGF-BB/aptamer　complex.　The　ECL　intensity　is　proportion　to　the　concentration　of　PDGF-BB　in　the　range　of　0.02-80　nM　with　a　detection　limit　of　0.013　nM.　This　work　demonstrates　a　simple　synthesis　method　to　obtain　QD@CNNS　with　excellent　ECL　behavior,　and　opens　up　the　application　of　g-C3N4　nanocomposite　in　signal-on　aptasensing.