The　development　of　environmentally　friendly,　simple　process　and　low　cost　synthesis　methods　for　preparing　graphene　nanosheets　(GNs)　has　attracted　global　interest.　In　this　work,　a　simple　and　efficient　method　to　synthesize　GNs　deriving　from　coal-tar　pitch　has　been　proposed　from　both　experimental　and　theoretical　point　of　views.　The　XRD,　TEM　and　Raman　results　demonstrate　that　precursor　Al4C3　could　provide　a　growth　environment　for　the　final　product　of　GNs.　Innovatively,　we　have　unraveled　the　microscopic　origin　for　the　decomposition　of　Al4C3　based　on　density　functional　theory　calculations.　It　is　highlighted　that　the　surface　energies　and　the　analysis　of　elastic　constants　indicate　the　fact　that　the　chemical　etching　process　in　Al4C3　can　happen,　which　is　similar　to　the　exfoliation　of　well-known　transition　metal　carbides　MXenes.　Furthermore,　different　bond　breaking　mechanisms　have　been　found　in　Al4C3　at　applied　tensile　and　shear　strains　from　the　electron　localization　functions　and　stress-strain　results.　Our　study　not　only　offers　an　efficient　method　to　synthesize　GNs,　but　also　to　unravel　the　microscopic　mechanism　of　fabrication　by　theoretical　calculations.